Rapid, low-sample-volume cholesterol and triglyceride assays

ABSTRACT

Reagents, assays, methods, kits, devices, and systems for rapid measurement of cholesterol and cholesterol sub-fractions from a blood sample are provided. Total cholesterol, low density lipoprotein cholesterol, and high density lipoprotein cholesterol can be measured in a single assay using kinetic measurements, under conditions in which cholesterol sub-species are converted to a detectable product at distinct rates. The detectable product is measured at different times after assay initiation. A lipase, cholesterol esterase, cholesterol oxidase and a peroxidase may be used together to produce colored product in amounts directly proportional to the quantity of cholesterol converted. Methods for calculating very-low density lipoprotein cholesterol levels by further including triglyceride measurements are disclosed. Assays may be performed in a single reaction mixture, allowing more accurate and precise cholesterol determinations, including ratios of cholesterol sub-fractions to total cholesterol, at less expense, than would be expected by performing several different assays in different reaction mixtures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, claims priority to, and the benefitunder 35 U.S.C. §120 of, U.S. patent application Ser. No. 14/100,870filed on Dec. 9, 2013, which application claims priority to, and thebenefit under 35 U.S.C. §119 of, U.S. Provisional Patent Application61/735,424 filed on Dec. 10, 2012, the disclosures of both of whichapplications are hereby incorporated by reference in their entireties.

BACKGROUND

Lipids, and in particular cholesterol, play a vital role in human healthand disease. Cholesterol is an essential nutrient and a criticalcomponent of lipid membranes which form the boundaries surrounding cellsand cellular organelles.

Excessive cholesterol, however, is very dangerous in that it canaccumulate as “plaques” in blood vessels and can cause thrombosis,stroke and other potentially lethal consequences in humans. To mitigatethese risks, lipids, especially cholesterol, are packaged intolipoproteins for transport through the body in blood.

Various heterogeneous forms of lipoproteins containing cholesterol (C)and triglycerides (TG) are known, including, for example, chylomicrons,very low density lipoprotein (VLDL), low density lipoprotein (LDL), andhigh density lipoprotein (HDL). The cholesterol content of theselipoproteins is termed VLDL-cholesterol (VLDL-C), LDL-cholesterol(LDL-C), and HDL-cholesterol (HDL-C), respectively.

Measurements or derived values of the cholesterol content of VLDL, LDL,HDL and the total cholesterol (TC) content of blood plasma or serum areroutinely made to assess the risk of atherosclerosis and the beneficialeffects of “cholesterol-lowering” drugs such as “statins”.

In prior art methods, centrifugation of blood samples providesdistinguishable VLDL, LDL and HDL fractions in blood serum or plasma;these fractions form distinct bands which move at different rates underthe centrifugal force because of their differing densities. Lipoproteinsalso can be separated by precipitation by use of differentialprecipitation using reagents such as dextran-sulfates,cyclodextrin-sulfates, and cations. For example, VLDL and LDL can becompletely precipitated while leaving all the HDL in solution. Once VLDLand LDL have been removed by centrifugation or filtration, the remainingcholesterol is associated only with the HDL fraction. Other prior artmethods may be used to estimate HDL-C and LDL-C which employ enzymesthat are modified, for example, by covalently attaching polyethyleneglycol (PEG) chains. The PEG is believed to restrict enzyme activity tospecific lipoprotein fractions. These prior art methods may also usespecific reagents which selectively solubilize or shield specificlipoprotein fractions so that only a single lipoprotein fraction isprecipitated or may react with assay chemistry in an assay.

In order for these cholesterol-content measurements to be valid, it isessential that they be very accurate and precise (error less than 5%)since small differences are clinically significant. Conventional meansfor measurement of cholesterol sub-fractions involve several independentassays (typically at least three, TC, LDL-C, and HDL-C) and/ormeasurement of three analytes (TC, TG, HDL-C) plus a calculated valuefor LDL-C using the Friedewald formula:

HDL-C≈TC−LDL-C−k×TG

Where “TG” is the triglyceride level, “x” indicates multiplication, and“k” is 0.2 for quantities measured in mg/dl (k is about 0.45 if thequantities are measured in mmol/1).

The Friedewald formula may be equivalently expressed in terms of LDL-Cas follows:

LDL-C≈TC−HDL-C−k×TG

Where again “TG” is the triglyceride level, “x” indicatesmultiplication, and “k” is 0.2 for quantities measured in mg/dl (k isabout 0.45 if the quantities are measured in mmol/1).

Of critical importance are the relative levels of the sub-forms oflipoprotein cholesterol: for example, the ratio of HDL-C to TC(HDL-C/TC), the ratio of LDL-C to TC (LDL-C/TC), or the ratio of VLDL-Cto TC (VLDL-C/TC). The levels of the sub-forms of lipoproteincholesterol are typically measured separately or by expensive andcumbersome physical separation methods such as centrifugation orelectrophoresis. Since these levels are conventionally measured inseveral independent assays each with its own sources of error, thecumulative error in the computed ratios of cholesterol sub-fractionswill be greater than that desired for effective diagnosis and monitoringof therapy. Additionally, the costs of analysis of lipoproteincholesterol sub-fractions are increased by the need for several assays.

INCORPORATION BY REFERENCE

All patents, patent applications, and publications mentioned herein arehereby incorporated by reference in their entireties.

SUMMARY

Applicants have found that very accurate and precise values for T-C,LDL-C and HDL-C can be obtained in a single assay for lipoproteincholesterol using kinetic measurements, without need for precipitationof lipoproteins and without separation steps. Assays as disclosed hereinuse a lipase (e.g., a cholesterol esterase), an oxidase (e.g., acholesterol oxidase) and a peroxidase to form a colored product. Assaysas disclosed herein may use a lipase (e.g., a cholesterol esterase), adehydrogenase (e.g., a cholesterol dehydrogenase) and nicotine adeninedinucleotide to form a light-absorbing product (e.g., NADH) or otherdetectable product. Such products may be measurable byspectrophotometry. In the assays disclosed herein, the amount of productformed from all the cholesterol-containing lipoprotein species isdirectly proportional to the quantity of cholesterol converted. Theassays, methods, reagents, and kits disclosed herein are useful forrapid, efficient, and inexpensive assays of lipoprotein cholesterol andlipoprotein cholesterol sub-fractions, and advantageously provide formeasurements of lipoprotein cholesterol and lipoprotein cholesterolsub-fractions in a single assay. Assays disclosed herein advantageouslyprovide for measurements of lipoprotein cholesterol and lipoproteincholesterol sub-fractions without need for lipoprotein precipitation.Assays disclosed herein advantageously provide for measurements oflipoprotein cholesterol and lipoprotein cholesterol sub-fractionswithout the need for centrifugation or for electrophoresis.

Applicants have found that it is possible to provide assay conditions(e.g., reagents, protocol and temperature) so that the kinetics ofreactions converting HDL-C, LDL-C and VLDL-C to colored product proceedat significantly different rates, while still allowing essentiallycomplete reaction of all lipoprotein species (e.g., HDL, LDL, and VLDL)by the end of the assay. For example, in assays disclosed herein thetime course for HDL-C has a half-time estimated at less than one minutewhereas the LDL-C conversion has a lag phase and an overall sigmoidshape centered on about three minutes. In assays disclosed herein, theremaining lipoprotein cholesterol (chylomicrons and VLDL-C) react evenmore slowly (half-time of about five minutes or longer). Thesedifferences in half-time and reaction kinetics between differentcholesterol species enable the de-convolution of an assay signal to thatattributable to each species using a simple algorithm even though, forexample, signal is being produced from more than one species duringcertain times during the assay. Accordingly, reagent formulations foruse in the assays and methods disclosed herein are designed to achievethe kinetic differentiation of lipoprotein species HDL, LDL, and VLDL ina single assay.

The novel methods and assays disclosed herein make use of Applicants'surprising finding that in these assays cholesterol sub-species areconverted to the measured product at distinct rates. Accordingly, HDL-Cis converted very rapidly to product, while LDL-C is converted toproduct more slowly than HDL-C is converted to product and VLDL-C andchylomicron cholesterol are converted even more slowly. Completeconversion of total cholesterol to product is even slower than theconversion of HDL-C or LDL-C to product. Such differences in rates ofconversion to product allow the measurement of cholesterol fromdifferent lipoprotein species to be made in a single solution atdifferent times, thus reducing the number of steps needed for suchmeasurements, reducing possible errors and simplifying the procedures.

Accordingly, Applicants disclose herein methods of determining HDL-C,LDL-C and TC in a single sample, or portion of a sample, of blood. Thesemethods allow determination of HDL-C, LDL-C and TC in a single sample,or portion of a sample, of blood without substantial precipitation oflipoproteins, e.g., without substantial precipitation of HDL or LDL inthe sample, or portion of a sample, of blood during the determination.As disclosed herein, the amount of HDL-C in a blood sample may bemeasured without substantial lipoprotein precipitation by colorimetricdetermination of the amount of peroxide formed in a first period of timefollowing combination of reagents effective to allow oxidation ofcholesterol released from lipoproteins in the sample. The first periodof time may be, for example, a period of time that is less than about 3minutes, and in embodiments may be a period of time of about 2 minutes.As disclosed herein, the amount of LDL-C in a blood sample may bemeasured without substantial lipoprotein precipitation by colorimetricdetermination of the amount of peroxide formed in a second period oftime following combination of reagents effective to allow oxidation ofcholesterol released from lipoproteins in the sample. In embodiments,the amount of LDL-C in a blood sample may be measured by the differencebetween colorimetric determinations made at the beginning of said secondperiod of time and colorimetric determinations made at the end of saidsecond period of time. The second period of time may be, for example, aperiod of time that is between about 2 minutes and about 6 minutesfollowing combination of reagents effective to allow oxidation ofcholesterol released from lipoproteins in the sample. As disclosedherein, the amount of TC in a blood sample may be measured withoutsubstantial lipoprotein precipitation by colorimetric determination ofthe amount of peroxide formed following combination of reagentseffective to allow oxidation of cholesterol released from lipoproteinsin the sample. This TC measurement (e.g., colorimetric determination)may be made at a time at the beginning of, or at any particular timeduring, a third period of time. The third period of time comprises aperiod of time after said second period of time, and may be, forexample, a period of time that begins about 6 minutes followingcombination of reagents effective to allow oxidation of cholesterolreleased from lipoproteins in the sample. For consistency of measurementbetween different samples, where different samples are measured indifferent determinations, the colorimetric determination for eachdifferent sample may be made at the same time after the beginning ofsaid third period of time for each sample.

Accordingly, HDL-C, LDL-C, and TC measurements may be made in a singlesample, or a single portion of a sample, of blood of a subject. Inembodiments, as disclosed herein, HDL-C, LDL-C, and TC measurements maybe made sequentially in a single sample, or a single portion of asample, of blood of a subject. For example, from these measurements, thelevel of VLDL-C in a single sample, or a single portion of a sample, ofblood of a subject may be calculated by the relationVLDL-C=TC−(HDL-C+LDL-C), or by other relationships. In embodiments, thelevel of VLDL-C in a single sample, or a single portion of a sample, ofblood of a subject may be calculated from these measurements, forexample, by a relation of the form VLDL-C=αTC+βHDL-C+γLDL-C+λ, where α,β, and γ are constants which multiply TC, HDL-C, and LDL-C,respectively; and where λ is an additive constants to be added to thesum of all other factors, respectively. In yet further embodiments, thelevel of VLDL-C in a single sample, or a single portion of a sample, ofblood of a subject may be calculated from other relationships using someor all of the measured values of TC, HDL-C, and LDL-C and multiplicativeand additive constants similar in form to the relationships providedabove.

Applicants thus disclose herein novel and useful measurements of HDL-C,LDL-C, and TC, and calculation of VLDL-C, which may be made on a singleblood sample, or portion of blood sample, reducing the amount of bloodneeded for such measurements, reducing the complexity of the methodsneeded to measure these different lipoprotein fractions in blood, andproviding accurate and rapid blood lipoprotein measurements. Thesemeasurements may be made without substantial precipitation oflipoproteins in the sample.

Applicants also disclose herein methods for determining triglyceridelevels in blood samples, where the level (equivalently: amount) oftriglyceride (TG) may be determined by methods in which a sample ofblood is contacted with a lipase, a kinase, and an oxidase to freeglycerol from TG in the blood sample, to phosphorylate the glycerol, andthen to provide hydrogen peroxide. The hydrogen peroxide, in thepresence of a peroxidase forms a colorant, the measurement of whichprovides a determination of the TG level in the blood sample.

Applicants disclose herein novel and useful measurements of HDL-C,LDL-C, TC, and TG which provide accurate and rapid blood lipoproteinmeasurements. The measurements of HDL-C, LDL-C and TC may be made on onesample or portion of sample of blood, while the TG measurements may bemade on a different sample or portion of sample of blood. Thesemeasurements may be made without substantial precipitation oflipoproteins in the samples. Together, these measurements of four bloodlipid components are made on only two samples, or two portions of asample or samples, of blood from a subject. Applicants disclose hereinfurther, improved methods for calculating VLDL-C in the blood of asubject, using HDL-C, TC, and TG measurements or using HDL-C, LDL-C, TC,and TG measurements. In embodiments, VLDL-C may be calculated fromHDL-C, TC, and TG measurements, or from HDL-C, LDL-C, TC, and TGmeasurements, where these measurements are made according to the methodsdisclosed herein. In embodiments, the level of VLDL-C in a singlesample, or a single portion of a sample, of blood of a subject may becalculated from these measurements, for example, by a relation of theform VLDL-C=αTC+βHDL-C+γLDL-C+δTG+a₁(TG+ε)(TC+κ)+λ, where α, β, γ, δ,and a₁ are constants which multiply TC, HDL-C, LDL-C, TG, and(TG+ε)(TC+κ), respectively; and where ε, κ, and λ are additive constantsto be added to TG, TC, and the sum of all other factors, respectively.In further embodiments, the level of VLDL-C in a single sample, or asingle portion of a sample, of blood of a subject may be calculated fromthese measurements, for example, by a relation of the formVLDL-C=αTC+βHDL-C+δTG+a₁(TG+ε)(TC+κ)+λ, where α, β, δ, and a₁ areconstants which multiply TC, HDL-C, TG, and (TG+ε)(TC+κ), respectively;and where ε, κ, and λ are additive constants to be added to TG, TC, andthe sum of all other factors, respectively. In yet further embodiments,the level of VLDL-C in a single sample, or a single portion of a sample,of blood of a subject may be calculated from other relationships usingsome or all of the measured values of TC, TG, HDL-C, and LDL-C andmultiplicative and additive constants similar in form to therelationships provided above.

In embodiments, reagent formulations for use in the assays and methodsdisclosed herein are designed to achieve the kinetic differentiationdescribed above without precipitation of lipoproteins. In reagents andassays disclosed herein, formation of complexes of lipoproteins withcations (optionally divalent cations such as magnesium, calcium,manganese, cobalt, cadmium, or other cations) and a negatively chargedpolysaccharide (such as, e.g., a dextran ester such as dextran-sulfate,a cyclodextrin ester such as α-cyclodextrin-sulfate, heparin, or othernegatively charged polysaccharide) is achieved in conditions where noprecipitation of lipoproteins occurs. For example, in embodiments,lipoprotein complex formation with magnesium ions and dextran sulfate isachieved in conditions where little or no precipitation of lipoproteinsoccurs. Amphiphilic compounds, such as surfactants may be included inreagents and assays disclosed herein. For example, a variety ofsurfactants are suitable for use in keeping the lipoproteins soluble. Inembodiments, the reagents provide ingredients effective to modify theLDL and VLDL lipoprotein particle surfaces in such a way as to restrictbut not prevent access (e.g., by cholesterol esterases and/or oxidases)to LDL and VLDL cholesterol and cholesterol esters. The use of reagentsand methods suitable for such modification of LDL and VLDL particlesurfaces is effective to slow the formation of colored product fromthese lipoprotein species as compared to the rate of formation ofcolored product in similar assays performed without the interactants andsurfactants, or with such agents at different concentrations andrelative proportions than are found in the assays and reagents disclosedherein. Slowing of the formation of colored product from lipoproteinspecies may be useful in order to provide separation of reactionkinetics effective to enable the measurement of cholesterol content ofdifferent lipoprotein fractions at different times without need forphysical separation of the different lipoprotein fractions (e.g.,without need for centrifugation or electrophoresis).

Accordingly, Applicants disclose herein a first reagent for use in anassay for the simultaneous, rapid measurement of at least two of totalcholesterol (TC), LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) ina sample of blood from a subject without substantial precipitation ofsaid blood lipoproteins, comprising a lipoprotein solubilization agentand a lipoprotein interactant. In embodiments, a first reagent maycomprise a buffer. In embodiments, a lipoprotein solubilization agentfor use in a first reagent as disclosed herein may comprise asurfactant. A lipoprotein interactant may comprise, for example, acyclodextrin, a dextran, or both. In embodiments, a lipoproteininteractant for use in such a first reagent may comprise a low molecularweight dextran. In embodiments, a lipoprotein interactant for use insuch a first reagent may comprise an α-cyclodextrin. In embodiments, afirst reagent may comprise a colorant. In embodiments, a first reagentmay include one or both of an aniline-containing compound and anaminoantipyrene compound, effective that both compounds, in the presenceof peroxide and a peroxidase, react to form a detectable product. Inembodiments of the reagents, assays, methods, and kits disclosed herein,such a first reagent may comprise α-cyclodextrin sulfate, dextransulfate, magnesium chloride, 4 aminoantipyrene and a buffer, such as aphosphate buffer. In embodiments of the reagents, assays, methods, andkits disclosed herein, such a first reagent may comprise α-cyclodextrinsulfate (1 mM), dextran sulfate (20 μM), magnesium chloride (4 mM), 4aminoantipyrene (2.25 mM) and Na_(x)PO₄ (100 mM) (where Na_(x)PO₄ is asodium phosphate salt; e.g., may be NaH₂PO₄, Na₂HPO₄, or Na₃PO₄). Inembodiments, the pH of such a first reagent may be between about pH 5and about pH 9, or between about pH 6 and about pH 8, optionally betweenabout pH 6.8 and about pH 7.8, e.g., about pH 7.4.

Applicants also disclose a second reagent for use in an assay for thesimultaneous, rapid measurement of at least two of total cholesterol(TC), LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) in a sample ofblood from a subject without substantial precipitation of said bloodlipoproteins, said second reagent comprising a lipase, an oxidase, and acolorant. In embodiments, a second reagent may comprise a buffer. Inembodiments of said second reagent, a lipase may comprise a cholesterolesterase, an oxidase may comprise a cholesterol oxidase, and a colorantmay comprise a peroxidase, a substrate for a peroxidase, or both. Inembodiments, both a peroxidase and a substrate for a peroxidase arepresent in said second reagent.

In embodiments, said second reagent may comprise a buffer, anamphiphilic agent, a cholesterol esterase, a cholesterol oxidase, and acolorant. In embodiments, an amphiphilic agent for use in such a secondreagent may comprise a surfactant. In embodiments, a colorant for use insuch a second reagent may comprise a peroxidase and a substrate for aperoxidase. In embodiments, a colorant for use in such a second reagentmay comprise horseradish peroxidase. In embodiments, a colorant for usein such a second reagent may comprise an aniline-containing compound,such as N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (ALPS),may comprise an aminoantipyrene compound, such as 4-aminoantipyrene, orother compounds and combinations of compounds which react with an enzymesuch as a peroxidase (e.g., horseradish peroxidase). In embodiments, asecond reagent may include both an aniline-containing compound and anaminoantipyrene compound, effective that both compounds, in the presenceof peroxide and a peroxidase, react to form a detectable product. Inembodiments, a lipase may comprise a cholesterol esterase. Inembodiments, a cholesterol esterase for use in such a second reagent maycomprise a bacterial cholesterol esterase, such as, for example, acholesterol esterase from a Pseudomonas bacterium. In embodiments, anoxidase may comprise a cholesterol oxidase. In embodiments, acholesterol oxidase for use in a second reagent as disclosed herein maycomprise a bacterial cholesterol oxidase, such as a cholesterol oxidasefrom a Pseudomonas bacterium. In embodiments of the reagents, assays,methods, and kits disclosed herein, such a second reagent may comprise abuffer, such as a phosphate buffer (e.g., Na_(x)PO₄ (where Na_(x)PO₄ isa sodium phosphate salt; e.g., may be NaH₂PO₄, Na₂HPO₄, or Na₃PO₄)),Triton X-100, pluronic L64,N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (ALPS), aPseudomonas cholesterol esterase, and a Pseudomonas cholesterol oxidase.For example, such a second reagent may comprise Na_(x)PO₄ (50 mM),Triton X-100 (0.06%), pluronic L64 (3 g/L),N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (ALPS) (3 mM),cholesterol esterase from Pseudomonas sp. (750 U/L), and cholesteroloxidase from Pseudomonas sp. (1.5 kU/L). In embodiments, the pH of sucha second reagent may be between about pH 5 and about pH 9, or betweenabout pH 6 and about pH 8, optionally between about pH 6.8 and about pH7.8, e.g., about pH 7.4.

Applicants disclose herein methods and reagents for use in a cholesterolassay, including second reagents comprising a lipase, an oxidase, and acolorant, said second reagents comprising a lipoprotein interactant at aconcentration level that, when used in methods disclosed herein,provides for conversion of HDL-C to a measureable colored product (orproduct measureable, e.g., in the near ultraviolet range of thespectrum) at a substantially different rate than for conversion of LDL-Cto a measureable colored product (or product measureable, e.g., in thenear ultraviolet range of the spectrum). Applicants disclose hereinmethods and reagents for use in a cholesterol assay comprising a lipase,an oxidase, and a colorant, including second reagents comprising alipoprotein interactant at a concentration level that, when used inmethods disclosed herein, provides for conversion of HDL-C to ameasureable colored product at a substantially different rate than forconversion of VLDL-C to a measureable colored product. Applicantsdisclose herein methods and reagents for use in a cholesterol assaycomprising a lipase, an oxidase, and a colorant, including secondreagents comprising a lipoprotein interactant at a concentration levelthat, when used in methods disclosed herein, provides for conversion ofLDL-C to a measureable colored product at a substantially different ratethan for conversion of VLDL-C to a measureable colored product.Applicants disclose herein methods and reagents for use in a cholesterolassay comprising a lipase, an oxidase, and a colorant, including secondreagents comprising a lipoprotein interactant at a concentration levelthat, when used in methods disclosed herein, provides for conversion ofHDL-C to a measureable colored product at a substantially different ratethan for conversion of LDL-C and/or VLDL-C to a measureable coloredproduct. Applicants disclose herein methods and reagents for use in acholesterol assay comprising a lipase, an oxidase, and a colorant,including second reagents comprising a lipoprotein interactant at aconcentration level that, when used in methods disclosed herein, providefor conversion of LDL-C to a measureable colored product at asubstantially different rate than for conversion of HDL-C and VLDL-C toa measureable colored product.

In embodiments, a colorant may comprise a peroxidase and a substrate fora peroxidase. For example, in embodiments, a colorant may comprise aperoxidase, an aniline-containing compound, and an aminoantipyrenecompound.

Applicants disclose herein reagents for use in a cholesterol assaycomprising a cholesterol esterase and a cholesterol oxidase, includingreagents comprising a lipoprotein interactant at a concentration levelthat provides for conversion of HDL-C to a measureable colored productat a substantially different rate than for conversion of LDL-C andVLDL-C to a measureable colored product, and provides for conversion ofHDL-C to a measureable colored product at a substantially different ratethan for conversion of LDL-C and VLDL-C to a measureable coloredproduct.

Applicants disclose herein reagents for use in a cholesterol assaycomprising a cholesterol esterase and a cholesterol oxidase, includingreagents comprising a negatively charged polysaccharide derivative and adivalent cation in concentrations effective that there is no substantialprecipitation of LDL, or that there is no substantial VLDLprecipitation, or both, when a sample of blood or a portion of a bloodsample contacts said reagent. Applicants disclose herein reagents foruse in a cholesterol assay comprising a cholesterol esterase and acholesterol oxidase, said reagents comprising a ratio of negativelycharged polysaccharide to divalent cations of between about 0.002 toabout 0.02, and in embodiments of about 0.005, effective that there isno substantial precipitation of HDL, or that there is no substantialprecipitation of LDL, or that there is no substantial precipitation ofVLDL, when a sample of blood or a portion of a blood sample contactssaid reagent. In embodiments, said reagent comprises a first reagent asdisclosed herein.

Applicants disclose herein reagents for use in a cholesterol assaycomprising a cholesterol esterase and a cholesterol oxidase, saidreagents comprising a negatively charged polysaccharide, a divalentcation, and surfactant in concentrations effective that there is nosubstantial precipitation of HDL, or that there is no substantialprecipitation of LDL, or that there is no substantial precipitation ofVLDL, when a sample of blood or a portion of a blood sample contactssaid reagent. In embodiments, said reagent comprises a first reagent asdisclosed herein.

Applicants disclose herein reagents for use in a cholesterol assaycomprising a cholesterol esterase and a cholesterol oxidase, saidreagents comprising dextran sulfate (or other negatively chargedpolysaccharide) and magnesium (or other divalent cation) inconcentrations effective that there is no substantial precipitation ofHDL, or that there is no substantial precipitation of LDL, or that thereis no substantial precipitation of VLDL, when a sample of blood or aportion of a blood sample contacts said reagent. Applicants discloseherein reagents for use in a cholesterol assay comprising a cholesterolesterase and a cholesterol oxidase, said reagents comprising a ratio ofdextran sulfate (or other negatively charged polysaccharide) tomagnesium ions (or other divalent cations) of between about 0.002 toabout 0.02, and in embodiments of about 0.005, effective that there isno substantial precipitation of HDL, or that there is no substantialprecipitation of LDL, or that there is no substantial precipitation ofVLDL, when a sample of blood or a portion of a blood sample contactssaid reagent or composition. Applicants disclose herein reagents for usein a cholesterol assay comprising a cholesterol esterase and acholesterol oxidase, said reagents comprising dextran sulfate,magnesium, and surfactant in concentrations effective that there is nosubstantial precipitation of LDL, or that there is no substantial VLDLprecipitation, or both, when a sample of blood or a portion of a bloodsample contacts said reagent or composition. In embodiments, saidreagent comprises a first reagent as disclosed herein.

Applicants further disclose herein a composition for use in an assay forthe simultaneous, rapid measurement of at least two of total cholesterol(TC), LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) in a sample ofblood from a subject without substantial precipitation of said bloodlipoproteins, comprising a lipoprotein solubilization agent, alipoprotein interactant, a lipase, an oxidase, and a colorant. Inembodiments, such a composition may comprise a buffer. In embodiments,the colorant comprises a peroxidase, an aniline-containing compound, andan aminoantipyrene compound. In embodiments, the composition includesingredients from the first reagent and the second reagent as disclosedherein. Such a composition may be provided, for example, by combinationof said first reagent and said second reagent as disclosed herein. Inembodiments, such a composition may comprise a negatively chargedpolysaccharide and a salt comprising a divalent cation (e.g., amagnesium salt and dextran sulfate), wherein the ratio of negativelycharged polysaccharide to divalent cation (e.g., dextran sulfate tomagnesium ions) is between about 0.002 to about 0.02, and in embodimentsthe ratio is about 0.005, effective that there is no substantialprecipitation of HDL, or that there is no substantial precipitation ofLDL, or that there is no substantial precipitation of VLDL, when asample of blood or a portion of a blood sample contacts saidcomposition. In embodiments, such a composition comprises said firstreagent and said second reagent, or an aliquot of said first reagent andan aliquot of said second reagent. In further embodiments, such acomposition comprises said first reagent, said second reagent, and asample of blood, or an aliquot or aliquots of one or more of said firstreagent, said second reagent, and said sample of blood.

In embodiments, a lipoprotein solubilization agent in such a compositionmay comprise a surfactant. In embodiments, a lipoprotein interactant insuch a composition may comprise a divalent cation (e.g., magnesium ion)and a negatively charged polysaccharide derivative. A negatively chargedpolysaccharide derivative may comprise a cyclodextrin-ester, adextran-ester, or both a cyclodextrin-ester and a dextran-ester. Forexample, a dextran-ester may comprise a low molecular weightdextran-ester, e.g., a low molecular weight dextran sulfate, and acyclodextrin-ester may comprise an α-cyclodextrin-ester, e.g.,α-cyclodextrin-sulfate. In embodiments, a lipase may comprise acholesterol esterase. In embodiments, an oxidase may comprise acholesterol oxidase. In embodiments, a colorant may comprise aperoxidase.

Accordingly, in embodiments, a composition for use in a cholesterolassay as disclosed herein may comprise a cholesterol esterase; acholesterol oxidase; a peroxidase; a substrate for a peroxidase; asurfactant; a salt containing a divalent cation; and a negativelycharged polysaccharide (e.g., a dextran derivative such as dextransulfate). In embodiments, a substrate for a peroxidase in such acomposition comprises both an aniline-containing compound and anaminoantipyrene compound, effective that both compounds, in the presenceof peroxide and a peroxidase, react to form a detectable product. Inembodiments, a substrate for a peroxidase may comprise other compoundsand combinations of compounds which react with a peroxidase (e.g.,horseradish peroxidase). An aniline-containing compound may be, forexample, N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline(ALPS). An aminoantipyrene compound may be 4-aminoantipyrene.

In embodiments, a composition for use in a cholesterol assay asdisclosed herein may comprise dextran sulfate (or other negativelycharged polysaccharide) and magnesium in concentrations effective thatthere is no substantial precipitation of HDL, or that there is nosubstantial precipitation of LDL, or that there is no substantialprecipitation of VLDL, when a sample of blood or a portion of a bloodsample contacts said composition. Applicants disclose hereincompositions for use in a cholesterol assay comprising a cholesterolesterase and a cholesterol oxidase, said compositions comprising a ratioof dextran sulfate to magnesium ions of between about 0.002 to about0.02, and in embodiments of about 0.005, effective that there is nosubstantial precipitation of HDL, or that there is no substantialprecipitation of LDL, or that there is no substantial precipitation ofVLDL, when a sample of blood or a portion of a blood sample contactssaid reagent. Applicants disclose herein compositions for use in acholesterol assay comprising a cholesterol esterase and a cholesteroloxidase, said compositions comprising dextran sulfate, magnesium, andsurfactant in concentrations effective that there is no substantialprecipitation of LDL, or that there is no substantial VLDLprecipitation, or both, when a sample of blood or a portion of a bloodsample contacts said composition.

In embodiments, a composition for use in an assay for the simultaneous,rapid measurement of at least two of total cholesterol (TC),LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) in a sample of bloodfrom a subject without substantial precipitation of said bloodlipoproteins may comprise a cholesterol esterase, a cholesterol oxidase,a peroxidase (such as horseradish peroxidase), 4-aminoantipyrene, ALPS,α-cyclodextrin sulfate, dextran sulfate, magnesium chloride, asurfactant (e.g., Triton X-100 and/or pluronic L64), and a buffer. Asuitable buffer may be, for example, a phosphate buffer, and a suitablepH may be in the range of between about pH 5 to about pH 9, or betweenabout pH 6 and about 8, optionally between about pH 6.8 and about pH7.8, e.g. about pH 7.4. A suitable cholesterol esterase for use in sucha composition may comprise a bacterial cholesterol esterase, such as,for example, a cholesterol esterase from a Pseudomonas bacterium, and asuitable cholesterol oxidase may comprise a bacterial cholesteroloxidase, such as a cholesterol oxidase from a Pseudomonas bacterium.

Applicants disclose herein a kit comprising reagents for use in an assayfor the simultaneous, rapid measurement of at least two of TC, LDL-C andHDL-C in a sample of blood from a subject without substantialprecipitation of said lipoproteins. Embodiments of the kits disclosedherein may comprise a first container containing a first reagentcomprising a lipoprotein solubilization agent, a lipoproteininteractant, and a buffer; and a second container containing a secondreagent comprising a buffer, an amphiphilic agent, a lipase, an oxidase,and a colorant. Embodiments of the kits disclosed herein may comprise afirst container containing a first reagent comprising a lipoproteinsolubilization agent, a lipoprotein interactant, and a buffer; and asecond container containing a second reagent comprising a buffer, anamphiphilic agent, a cholesterol esterase, a cholesterol oxidase, and acolorant. In embodiments, a colorant may comprise a peroxidase, asubstrate for a peroxidase, or both.

Embodiments of the kits disclosed herein may comprise a first containercontaining a first reagent comprising a lipoprotein solubilizationagent, a lipoprotein interactant, and a buffer; a second containercontaining a second reagent comprising a buffer, an amphiphilic agent, alipase, an oxidase, and a colorant; and instructions for their use. Inembodiments, such kits comprise a first container containing a firstreagent comprising a lipoprotein solubilization agent, a lipoproteininteractant, and a buffer; a second container containing a secondreagent comprising a buffer, an amphiphilic agent, a cholesterolesterase, a cholesterol oxidase, and a colorant; and instructions fortheir use. In embodiments, a colorant may comprise a peroxidase and asubstrate for a peroxidase.

Also disclosed herein are methods for the simultaneous, rapidmeasurement of at least two of TC, LDL-C and HDL-C in a sample of bloodfrom a subject without substantial precipitation of said lipoproteins.Embodiments of methods for the simultaneous, rapid measurement of TC,LDL-C and HDL-C in a sample of blood from a subject without substantialprecipitation of said lipoproteins comprise steps of: combining at aninitial time at least a portion of said sample of blood with a firstreagent comprising a lipoprotein solubilization agent, a lipoproteininteractant, and a buffer to provide a combined solution; adding to saidcombined solution a second reagent comprising a buffer, an amphiphilicagent, a lipase, an oxidase, and a colorant to provide a coloredsolution; and measuring absorbance of light by said colored solutionwithin a first time period, within a second time period, and within athird time period after addition of said second reagent.

In embodiments of such methods, said first time period comprises a timeperiod of less than about 3 minutes after said initial time, and saidthird time period comprises a time period of greater than about 5minutes after said initial time, where said initial time comprises thetime at which said second reagent is added to said combined solution.

In embodiments, said methods for the simultaneous, rapid measurement ofTC, LDL-C and HDL-C in a sample of blood from a subject withoutsubstantial precipitation of said lipoproteins comprise steps of:combining at an initial time at least a portion of said sample of bloodwith a first reagent comprising a lipoprotein solubilization agent, alipoprotein interactant, and a buffer to provide a combined solution;adding to said combined solution a second reagent comprising a buffer,an amphiphilic agent, a cholesterol esterase, a cholesterol oxidase, anda colorant to provide a colored solution; and measuring absorbance oflight by said colored solution within a first time period, within asecond time period, and within a third time period.

In embodiments of such methods, said first time period comprises a timeperiod of less than about 3 minutes after said initial time, and saidthird time period comprises a time period of greater than about 5minutes after said initial time, where said initial time comprises thetime at which said second reagent is added to said combined solution.

In embodiments of the methods disclosed herein, the first time periodmay comprise a time period of between about 0 minutes to about 2 minutesafter said initial time, the second time period may comprise a timeperiod of between about 2 minutes to about 6 minutes after said initialtime, and the third time period may comprise a time period of betweenabout 6 minutes to about 10 minutes, or longer. In embodiments, saidthird time period comprises an open-ended time period including any timeafter about 5 minutes or about 6 minutes after said initial time. Inembodiments, the initial time is the time at which the second reagent isadded to the solution.

It will be understood that other times and time periods may also beused, e.g., longer times and time periods may be used where the amountsof lipase, or oxidase, or both, are decreased. It will also beunderstood that, e.g., shorter times and time periods may be used wherethe amounts of lipase, or oxidase, or both, are increased. Similarly,other times and time periods may also be used where the amounts oflipoprotein solubilization agents and/or lipoprotein interactants arealtered. Accordingly, in further embodiments of the methods disclosedherein, the time periods may be longer than the time periods discussedabove; for example, reagents and methods may be configured where thefirst time period may comprise a time period of between about 0 minutesto about 10 minutes after said initial time, the second time period maycomprise a time period of between about 10 minutes to about 20 minutesor about 30 minutes after said initial time, and the third time periodmay comprise a time period of between about 20 minutes to about 40minutes, or between about 30 minutes to about 60 minutes, or longer. Inyet further embodiments of the methods disclosed herein, the timeperiods may be shorter than the time periods discussed above; forexample, reagents and methods may be configured where the first timeperiod may comprise a time period of between about 0 minutes to about 1minute after said initial time, the second time period may comprise atime period of between about 1 minutes to about 4 minutes or to about 5minutes after said initial time, and the third time period may comprisea time period of between about 4 minutes to about 8 minutes, or betweenabout 5 minutes to about 9 minutes.

In embodiments, a step of measuring absorbance may comprise measuringabsorbance using a spectrophotometer. A step of measuring absorbancewill typically comprise measuring absorbance at or near a particularfrequency using a spectrophotometer. In embodiments, a step of measuringabsorbance may comprise measuring absorbance at or near a wavelength ofabout 560 nm. In embodiments, a step of measuring absorbance may furthercomprise using a spectrophotometer to measure the difference inabsorbance at or near to a first wavelength and the absorbance at ornear to a second wavelength; such a difference in absorbance measured attwo wavelengths may be termed “ΔA.” For example, such two wavelengthsmay be about 560 nm and about 700 nm. In embodiments, a step ofmeasuring absorbance may further comprise using a spectrophotometer tomeasure absorbance at a wavelength of about 560 nm and at a wavelengthof about 700 nm effective to obtain the difference in absorbance betweenabout 560 nm and about 700 nm. It will be understood that for somecolorants, other wavelengths, and other wavelength intervals, may beused; for example, there are chromogenic peroxidase substrates that maybe detected at wavelengths between about 400 nm and about 700 nm.

Such absorbance measurements may be made at a particular time, or at twoparticular times, or at three, or more, particular times, where aparticular time is defined with respect to an initial time. Measurementsat a particular time may include measurements made during a range oftimes, such as between 0 to about 2 minutes after an initial time, orbetween about 2 minutes and about 6 minutes after an initial time, orbetween about 6 minutes and about 10 minutes after an initial time, orat other times and/or other time periods.

In embodiments, a step of measuring absorbance may comprise measuringabsorbance using a spectrophotometer at two times, and recording orcalculating the difference between the measurements made at said twotimes. In embodiments, absorbance may be ΔA measured as the differencein absorbance measured at two wavelengths, and the difference of the ΔAmeasured at a first time and the ΔA measured at a second time may berecorded or calculated; such a difference between ΔA measured at twotimes may be termed “ΔA_(t).” For example, ΔA_(t) may be measured bymeasuring ΔA as the difference between absorbance measured at 560 nm andat 700 nm, where the ΔA measurement is made at about 2 minutes after aninitial time and at about 6 minutes after an initial time, where ΔA_(t)is the difference between the two ΔA measurements. In furtherembodiments, ΔA_(t) may be measured by measuring ΔA as the differencebetween absorbance measured at 560 nm and at 700 nm, where the ΔAmeasurement is made at an initial time and at about 2 minutes after aninitial time, where ΔA_(t) is the difference between the two ΔAmeasurements. In further embodiments, ΔA_(t) may be measured bymeasuring ΔA as the difference between absorbance measured at 560 nm andat 700 nm, where the ΔA measurement is made at about 6 minutes after aninitial time and at about 10 minutes after an initial time, where ΔA_(t)is the difference between the two ΔA measurements. In furtherembodiments, where the ΔA measurement is to be made after a particulartime, it will be understood that phrases such as, e.g., “after about 5minutes”, “after about 10 minutes”, “at a time period greater than about5 minutes”, “at a time period greater than about 10 minutes”, and thelike, may be measured between any time after the stated time and areasonable time thereafter. In embodiments, such a time period formeasurement may not extend in time beyond about 30 minutes, or beyondabout 20 minutes, after the initial time.

In embodiments, a first reagent may comprise a lipoproteinsolubilization agent, a lipoprotein interactant, and a buffer. Inembodiments, a lipoprotein solubilization agent may comprise asurfactant. In embodiments, a lipoprotein interactant may comprise adextran (such as a dextran derivative such as a sulfonated orphosphorylated dextran), a cyclodextrin (such as a cyclodextrinderivative such as a sulfonated or methylated cyclodextrin), anegatively charged natural product such as heparin, or combinationsthereof. In embodiments, a lipoprotein interactant may comprise a lowmolecular weight negatively charged dextran ester, e.g., a low molecularweight dextran sulfate. In embodiments, a lipoprotein interactant maycomprise an α-cyclodextrin derivative such as an α-cyclodextrin sulfateester. In embodiments, a first reagent may comprise a peroxidasesubstrate. In embodiments, a peroxidase substrate may comprise anaminoantipyrene compound, such as 4-aminoantipyrene and ananiline-containing compound, such as ALPS. In further embodiments, thefirst reagent may comprise α-cyclodextrin sulfate, dextran sulfate,magnesium chloride, 4-aminoantipyrene, ALPS, and a buffer, such as, forexample, a phosphate buffer (e.g., Na_(x)PO₄ (where Na_(x)PO₄ is asodium phosphate salt; e.g., may be NaH₂PO₄, Na₂HPO₄, or Na₃PO₄) forbuffering the pH to between about pH 6 to about pH 8. For example, inembodiments, the first reagent may comprise α-cyclodextrin sulfate (1mM), dextran sulfate (20 μM), magnesium chloride (4 mM),4-aminoantipyrene (2.25 mM), 3 mM ALPS, and Na_(x)PO₄ (100 mM), pH about7.

In embodiments, components of a peroxidase substrate may be separatedinto different reagents. Separation of peroxidase substrate componentsinto different reagents may be desired for stability of one or both ofthe reagents, or may be useful to reduce or prevent degradation of oneor both of the reagents. Thus, in embodiments, a first reagent mayinclude an antipyrene compound, and a second reagent may include ananiline-containing compound. In further embodiments, a first reagent maycomprise 4-aminoantipyrene and a second reagent may compriseN-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (ALPS). Infurther embodiments, a first reagent may comprise between about 1 mM andabout 5 mM 4-aminoantipyrene and a second reagent may comprise betweenabout 0.5 mM and about 20 mM ALPS. For example, a first reagent maycomprise 2.25 mM 4-aminoantipyrene and a second reagent may comprise 3mM ALPS.

In embodiments, components of a peroxidase substrate may be contained ina single reagent. Including multiple components in a single reagent maybe desired for simplicity of manufacture, or ease of use, or for otherreasons. For example, a reagent containing all components of aperoxidase substrate may comprise an aminoantipyrene compound and ananiline-containing compound. In further embodiments, a reagentcontaining all components of a peroxidase substrate may comprise4-aminoantipyrene andN-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (ALPS). Infurther embodiments, a reagent containing all components of a peroxidasesubstrate may comprise between about 1 mM and about 5 mM4-aminoantipyrene and between about 0.5 mM and about 20 mM ALPS. Forexample, a reagent containing all components of a peroxidase substratemay comprise 2.25 mM 4-aminoantipyrene and 3 mM ALPS. In otherembodiments, reagents may be dried so as to increase stability. Reagentsmay be lyophilized or provided as glassy films, e.g., films which mayadhere to a container wall. When such reagents are dried, they may beformulated so as to dissolve rapidly (e.g., within seconds to minutes)upon addition of water or of another aqueous solvent such as a buffersolution.

In embodiments of the methods disclosed herein, a second reagent maycomprise a lipase, an oxidase, and a colorant. In embodiments of saidsecond reagent, a lipase may comprise a cholesterol esterase, an oxidasemay comprise a cholesterol oxidase, and a colorant may comprise aperoxidase. In embodiments of the methods disclosed herein, a secondreagent may comprise a buffer, an amphiphilic agent, a cholesterolesterase, a cholesterol oxidase, and a colorant. In embodiments of themethods disclosed herein, an amphiphilic agent may comprise asurfactant. In embodiments, a colorant may comprise a peroxidase, aperoxidase substrate, and may comprise both a peroxidase and aperoxidase substrate. A peroxidase may comprise, for example, aperoxidase from horseradish (Armoracia rusticana) (HRP). A peroxidasesubstrate may comprise an aniline-containing compound, anaminoantipyrene compound or both. In embodiments, a colorant maycomprise an aminoantipyrene compound, such as 4-aminoantipyrene. Inembodiments, a colorant may compriseN-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (ALPS). Inembodiments of the methods disclosed herein, a second reagent maycomprise a bacterial cholesterol esterase, such as a cholesterolesterase from a Pseudomonas bacterium, and in embodiments may comprise abacterial cholesterol oxidase, such as a bacterial cholesterol oxidasefrom a Pseudomonas bacterium. In embodiments of the methods disclosedherein, a second reagent may comprise a buffer, such as a phosphatebuffer (e.g., Na_(x)PO₄ (50 mM)), Triton X-100 (0.06%), pluronic L64 (3g/L), N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (ALPS) (3mM), cholesterol esterase from Pseudomonas sp. (750 U/L), andcholesterol oxidase from Pseudomonas sp. (1.5 kU/L).

In embodiments, a composition as disclosed herein may compriseα-cyclodextrin sulfate, dextran sulfate, magnesium chloride, aperoxidase substrate (e.g., diaminobenzidine, or 4-aminoantipyrene andALPS), cholesterol esterase (e.g., cholesterol esterase from Pseudomonassp.), cholesterol oxidase (e.g., cholesterol oxidase from Pseudomonassp.), a surfactant, and a buffer. In embodiments, a composition asdisclosed herein may comprise a first reagent and a second reagent. Inembodiments, a composition as disclosed herein may comprise a firstreagent, a second reagent, and at least a portion of a sample of bloodfrom a subject.

A buffer, for example, may be a phosphate buffer (e.g., Na_(x)PO₄ (whereNa_(x)PO₄ is a sodium phosphate salt; e.g., may be NaH₂PO₄, Na₂HPO₄, orNa₃PO₄) for buffering the pH to between about pH 5 to about pH 9, orbetween about pH 6 to about pH 8, optionally between about pH 6.8 toabout pH 7.8, e.g., pH 7.4. In embodiments, a composition as disclosedherein may comprise between about 100 U/L to about 2000 U/L ofcholesterol esterase from Pseudomonas sp. (e.g., about 750 U/L), and maycomprise between about 100 U/L to about 3000 U/L cholesterol oxidasefrom Pseudomonas sp. (e.g., about 1.5 kU/L).

In embodiments, for example, a peroxidase substrate may comprise betweenabout 1 mM and about 5 mM 4-aminoantipyrene and between about 0.5 mM andabout 20 mM ALPS, e.g., about 2.25 mM 4-aminoantipyrene and about 3 mMALPS. In embodiments, a surfactant may be, for example, Triton X-100and/or pluronic L64, e.g., the composition may comprise about 0.01 toabout 1% Triton X-100 and may comprise about 1 to about 10 g/L/orpluronic L64; in particular embodiments, the composition may compriseabout 0.06% Triton X-100 and about 3 g/L pluronic L64.

In embodiments of the methods disclosed herein, a measurement within afirst time period may be used to determine HDL-cholesterol in saidsample. In embodiments of the methods disclosed herein, a measurementwithin a second time period may be used to determine LDL-cholesterol insaid sample. In embodiments of the methods disclosed herein, ameasurement within a third time period may be used to determine totalcholesterol in said sample. In embodiments of the methods disclosedherein, a measurement may comprise measuring absorbance using aspectrophotometer. In embodiments of the methods disclosed herein, ameasurement may comprise measuring ΔA (where ΔA is the differencebetween absorbance measured at the first wavelength and at the secondwavelength) using a spectrophotometer. In embodiments of the methodsdisclosed herein, a measurement may comprise measuring ΔA_(t) (whereΔA_(t) is the difference between absorbance measured at a first time andthe absorbance measured at a second time) using a spectrophotometer.Absorbance measurements for measuring ΔA_(t) may be ΔA measurements.

In embodiments of the methods disclosed herein, a method of analyzingcholesterol measurement data obtained from a blood sample of a subjectmay comprise steps of: measuring product formation from a reactionbetween cholesterol sub-fractions and a reagent mixture comprising alipase and an oxidase within a first time period, within a second timeperiod, and within a third time period to provide cholesterolmeasurement data; wherein a low density lipoprotein-cholesterol (LDL-C)measurement is obtained from said cholesterol measurement data obtainedwithin said second time period; wherein a total cholesterol (TC)measurement is obtained from said cholesterol measurement data obtainedwithin said third time period; and wherein a high densitylipoprotein-cholesterol (HDL-C) measurement is obtained from saidcholesterol measurement data obtained within said second time periodplus the rate of product formation measured in said first time period;whereby said cholesterol measurement data obtained from a blood sampleof a subject is analyzed.

In particular embodiments of the methods of analyzing cholesterolmeasurement data obtained from a blood sample of a subject disclosedherein, said lipase may comprise a cholesterol esterase, and saidoxidase may comprise a cholesterol oxidase. For example, in embodimentsof the methods disclosed herein, a method of analyzing cholesterolmeasurement data obtained from a blood sample of a subject may comprisesteps of: measuring product formation from a reaction betweencholesterol sub-fractions and a reagent mixture comprising a cholesterolesterase and a cholesterol oxidase within a first time period, within asecond time period, and within a third time period to providecholesterol measurement data; wherein a LDL-C measurement is obtainedfrom said cholesterol measurement data obtained within said second timeperiod; wherein a TC measurement is obtained from said cholesterolmeasurement data obtained within said third time period; and wherein aHDL-C measurement is obtained from said cholesterol measurement dataobtained within said second time period plus the rate of productformation measured in said first time period; whereby said cholesterolmeasurement data obtained from a blood sample of a subject is analyzed.

Embodiments of a method of analyzing cholesterol measurement dataobtained from a blood sample of a subject may comprise steps whereinsaid first time period may comprise less than about 3 minutes after aninitial time, wherein said initial time comprises the time at which asecond reagent is added to a combined solution, and wherein a combinedsolution may comprise a first reagent and at least a portion of a bloodsample. In embodiments, a method of analyzing cholesterol measurementdata obtained from a blood sample of a subject may comprise a stepwherein a third time period comprises a time period of greater thanabout 5 minutes after said initial time, wherein said initial timecomprises the time at which a second reagent is added to a combinedsolution. In embodiments, said first time period comprises a time periodof between about 0 minutes to about 2 minutes after said initial time,said second time period comprises a time period of between about 2minutes to about 6 minutes after said initial time, and said third timeperiod comprises a time period of between about 6 minutes to about 10minutes, or longer. In embodiments, said third time period may comprisean open-ended time period, effective to include any time greater thanabout 5 minutes after said initial time, or greater than about 6 minutesafter said initial time.

In embodiments, a step of measuring product formation comprisesmeasuring absorbance. In embodiments, a step of measuring absorbancecomprises measuring ΔA using a spectrophotometer. In furtherembodiments, a step of measuring absorbance using a spectrophotometercomprises measuring absorbance at a first wavelength and measuringabsorbance at a second wavelength to obtain a ΔA measurement, where ΔAis the difference between absorbance measured at the first wavelengthand at the second wavelength. In embodiments, a step of measuring ΔAusing a spectrophotometer comprises measuring ΔA at a wavelength ofbetween about 300 nm to about 700 nm, and at a wavelength of betweenabout 600 nm to about 900 nm. In more particular embodiments, a step ofmeasuring ΔA using a spectrophotometer comprises measuring ΔA at awavelength of about 560 nm and at a wavelength of about 700 nm.

In at least some embodiments, methods disclosed herein include furthermethods of analyzing cholesterol measurement data obtained from a bloodsample of a subject, wherein an HDL-C measurement is obtained from saidcholesterol measurement data obtained within a second time period plusthe rate of product formation measured in a first time period accordingto the following formula:

K₁−K₂×(LDL-C)+K₃×R₁

-   -   where K₁ is a constant whose value may be between about 0 to        about 250;    -   where K₂ is a constant whose value may be between about 0 to        about 100;    -   where the amount of LDL-C may be determined by the difference in        absorbance measured between the beginning of said second time        period and the end of said second time period;    -   where K₃ is a constant whose value may be between about 1 to        about 20,000; and    -   where R₁ may be determined by the difference in absorbance        measured between the beginning of said first time period and the        end of said first time period, and wherein said time periods may        be determined with respect to an initial time, wherein the        initial time period comprises the time at which a second reagent        is added to a combined solution comprising a first reagent and        at least a portion of said blood sample.        In embodiments, the value of K₁ may be between about 0 to about        100, or between about 0 to about 50. In embodiments, the value        of K₂ may be between about 0 to about 50, or between about 0 to        about 25. In embodiments, the value of K₃ may be between about 0        to about 10,000, or between about 0 to about 5,000. In further        embodiments, the value of K₁ may be between about 0 to about 25,        or between about 0 to about 10. In further embodiments, the        value of K₂ may be between about 0 to about 5, or between about        0 to about 2.

In embodiments of further methods of analyzing cholesterol measurementdata obtained from a blood sample of a subject, a first time period maycomprise a time period of between about 0 minutes to about 2 minutesafter an initial time. In embodiments, a second time period may comprisea time period of between about 2 minutes to about 6 minutes after aninitial time. In embodiments, a third time period may comprise a timeperiod of between about 6 minutes to about 10 minutes after an initialtime, or longer. In embodiments, said third time period may comprise anopen-ended time period, effective to include any time greater than about5 minutes after said initial time, or greater than about 6 minutes aftersaid initial time.

In embodiments of further methods of analyzing cholesterol measurementdata obtained from a blood sample of a subject, K₁ may have a valuebetween about 0 to about 3. In embodiments of further methods ofanalyzing cholesterol measurement data obtained from a blood sample of asubject, K₂ may have a value between about 0 to about 1. In embodimentsof further methods of analyzing cholesterol measurement data obtainedfrom a blood sample of a subject, K₃ may have a value between about 800to about 1,800. In embodiments of further methods of analyzingcholesterol measurement data obtained from a blood sample of a subject,K₁ may have a value of about 1.30. In embodiments of further methods ofanalyzing cholesterol measurement data obtained from a blood sample of asubject, K₂ may have a value of about 0.446. In embodiments of furthermethods of analyzing cholesterol measurement data obtained from a bloodsample of a subject, K₃ may have a value of about 1255.

In embodiments of further methods of analyzing cholesterol measurementdata obtained from a blood sample of a subject, cholesterol measurementdata may comprise data from an absorbance measurement. In embodiments offurther methods of analyzing cholesterol measurement data obtained froma blood sample of a subject, absorbance measurements may compriseabsorbance measurements made using a spectrophotometer. In embodimentsof further methods of analyzing cholesterol measurement data obtainedfrom a blood sample of a subject, an absorbance measurement using aspectrophotometer may comprise a ΔA measurement, where a ΔA measurementcomprises an absorbance measurement made at a first wavelength and anabsorbance measurement made at a second wavelength, effective to obtainthe difference in absorbance at said first wavelength and at said secondwavelength. In embodiments of further methods of analyzing cholesterolmeasurement data obtained from a blood sample of a subject, ameasurement of ΔA using a spectrophotometer may comprise absorbancemeasurements at a wavelength of about 560 nm and at a wavelength ofabout 700 nm.

Applicants further disclose herein devices for measuring totalcholesterol or a cholesterol sub-fraction in at least a portion of asample of blood from a subject. In embodiments, a device for measuringtotal cholesterol or a cholesterol sub-fraction in at least a portion ofa sample of blood from a subject may comprise: means for combining afirst reagent with at least a portion of a sample of blood from asubject, effective to provide a combined solution; means for combining asecond reagent with said combined solution to provide a coloredsolution; means for measuring an optical property of said coloredsolution; and means for displaying or reporting the results of saidmeasurement of said optical property of said colored solution. Infurther embodiments, a device for measuring total cholesterol or acholesterol sub-fraction in at least a portion of a sample of blood froma subject may comprise: a chamber for combining a first reagent with atleast a portion of a sample of blood from a subject, effective toprovide a combined solution; a conduit for combining a second reagentwith said combined solution to provide a colored solution; an opticaldetector for measuring an optical property of said colored solution; anda display element or a communication link for reporting the results ofsaid measurement of said optical property of said colored solution. Inembodiments, a display element and/or communication link may be suitablefor two-way communication.

Applicants disclose herein systems for measuring total cholesterol or acholesterol sub-fraction in at least a portion of a sample of blood froma subject. In embodiments, a system for measuring total cholesterol or acholesterol sub-fraction in at least a portion of a sample of blood froma subject comprises a device as disclosed herein, and a means forcommunicating information from said device to a computer, a computernetwork, a telephone, a telephone network, or a device configured todisplay information communicated from said device. It will be understoodthat a means for communicating information may include means for one-waycommunication and may include means for two-way communication, and mayinclude means for communication with multiple locations or entities. Inembodiments, a system for measuring total cholesterol or a cholesterolsub-fraction in at least a portion of a sample of blood from a subjectcomprises a device as disclosed herein, and a channel for communicatinginformation from said device to a computer, said wherein said channel isselected from a computer network, a telephone network, a metalcommunication link, an optical communication link, and a wirelesscommunication link. It will be understood that a channel forcommunicating information may be a one-way communication channel and maybe a two-way communication channel, and may include channels forcommunication with multiple locations or entities.

In embodiments, triglyceride levels may be determined by methods inwhich a sample of blood is contacted with a lipase to provide fattyacids and glycerol from TG in the blood sample. This glycerol may becontacted with a kinase, such as glycerol kinase, to provide glycerolphosphate, which may be contacted with an oxidase, such as glycerol3-phosphate oxidase, to provide dihydroxyacetone phosphate and hydrogenperoxide. Colorants, such as 4-aminoantipyrene andN-Ethyl-N-(sulfopropyl aniline) may be contacted with horseradishperoxidase in the presence of the hydrogen peroxide effective to form adye, such as a quinoneimine dye, the measurement of which dye provides ameasure of the TG level in the blood sample. Such a dye may be measuredby spectrophotometric means; for example, such a dye may be measured,and TG levels determined, by measuring absorbance at a frequency (e.g.,560 nm), or within a frequency range (e.g., 555 nm to 565 nm).

VLDL-C may be estimated from TG measurements by dividing theconcentration of TG in a sample by 5:

VLDL-C=TG/5

in order to provide a value for the level of VLDL-C in blood sample inwhich TG has been measured. The level of VLDL-C estimated in this waymay further be used to calculate the TC in a blood sample by adding thelevels of HDL-C, LDL-C, and VLDL-C (as estimated according to theformula VLDL-C=TG/5).

However, in place of such an estimate, Applicants disclose hereinfurther methods to calculate VLDL-C based on the novel and usefulmeasurements of HDL-C, LDL-C, TC, and TG disclosed herein. These furthermethods are believed to provide greater accuracy than prior methods. Inembodiments, VLDL-C may be calculated from HDL-C, TC, and TGmeasurements, where these measurements are made according to the methodsdisclosed herein. In embodiments, VLDL-C may be calculated from HDL-C,LDL-C, TC, and TG measurements, where these measurements are madeaccording to the methods disclosed herein.

In embodiments, the level of VLDL-C in a single sample, or a singleportion of a sample, of blood of a subject may be calculated from HDL-C,TC, and TG measurements, for example, by the relation:

VLDL-C=αTC+βHDL-C+δTG+a ₁(TG+ε)(TC+κ)+λ

where α, β, δ, and a₁ are constants which multiply TC, HDL-C, TG, and(TG+ε)(TC-κ), respectively; and where ε, κ, and λ are additive constantsto be added to TG, TC, and the sum of all other factors, respectively.The term “(TG+ε)(TC+κ)” may be called a “cross-term” in which the termsin one parenthesis multiply the terms in the other parenthesis. Themultiplicative constants α, β, δ, and a₁ and the additive constants ε,κ, and λ may take any value, whether positive, negative, or zero.

In embodiments, the level of VLDL-C in a single sample, or a singleportion of a sample, of blood of a subject may be calculated from HDL-C,LDL-C, TC, and TG measurements, for example, by the relation:

VLDL-C=αTC+βHDL-C+γLDL-C+δTG+a ₁(TG+ε)(TC+κ)+λ

where α, β, γ, δ, and a₁ are constants which multiply TC, HDL-C, LDL-C,TG, and (TG+ε)(TC+κ), respectively; and where ε, κ, and λ are additiveconstants to be added to TG, TC, and the sum of all other factors,respectively. The multiplicative constants α, β, γ, δ, and a₁ and theadditive constants ε, κ, and λ may take any value, whether positive,negative, or zero. As indicated above, and as used elsewhere herein, theterm “(TG+ε)(TC+κ)” and similar terms may be called a “cross-term” inwhich the terms in one parenthesis multiply the terms in the otherparenthesis.

It will be understood that, in embodiments, all possible cross-terms,and all possible combinations of cross-terms may be included inrelationships used to calculate VLDL-C. Thus, for example, in additionto, and/or in place of, the cross-term (TG+ε)(TC+κ), any or all of thefollowing cross-terms may be included in relationships used to calculateVLDL-C: (TG+ε)(HDL-C+μ); (TG+ε)(LDL-C+ν); (TC+κ)(HDL-C+μ);(TC+κ)(LDL-C+ν); and (LDL-C+ν)(HDL-C+μ), where the additive constants λ,ε, κ, μ, and ν may take any value, whether positive, negative, or zero.

Accordingly, in embodiments, VLDL-C may be calculated from the measuredquantities as follows:

VLDL-C=αTC+βHDL-C+γLDL-C+δTG++a ₁(TG+ε)(TC+κ)+a ₂(TG+ε)(HDL-C+μ)+a₃(TG+ε)(LDL-C+ν)+a ₄(TC+κ)(HDL-C+μ)+a ₅(TC+κ)(LDL-C+ν)+a₆(LDL-C+ν)(HDL-C+μ)

-   -   where the multiplicative coefficients α, β, γ, δ, a₁, a₂, a₃,        a₄, a₅, and a₆, may take any value, whether positive, negative,        or zero; and    -   where the additive constants λ, ε, κ, μ, and ν may take any        value, whether positive, negative, or zero.

In yet further embodiments, the level of VLDL-C in a single sample, or asingle portion of a sample, of blood of a subject may be calculated fromother relationships using some or all of the measured values of TC, TG,HDL-C, and LDL-C and multiplicative and additive constants similar inform to the relationships provided above.

Applicants further disclose herein methods, devices and systems formeasuring, in one device, at least two biologically relevant attributesof a sample. In embodiments, a biologically relevant attribute of asample includes, without limitation, a lipoprotein level including TC,HDL-C, LDL-C, and VLDL-C; blood triglyceride (TG) level; bloodhematocrit; blood iron content; erythrocyte sedimentation rate (ESR); acytometric measurement (e.g., determination of the presence and/oramounts, including fractional amounts and/or absolute amounts of a celltype or cell types) including antibody based, dye-based,flow-cytometric, imaging, and other measurements of cells, cell number,cell type, and cellular properties in a sample; a chemical measurementincluding a measurement of pH, of a salt concentration (e.g., of acation and/or anion which makes up a salt), presence of and/orconcentration of a vitamin, a protein, a metabolite of a protein orsmall molecule, a marker indicative of a medical condition, and othermeasurements of blood, urine, tissue, or other biological sample. Themeasurements of at least two biologically relevant attributes of asample may be made simultaneously, or may be made in succession, or,where at least three measurements of biologically relevant attributes ofa sample are made, some measurements may be made simultaneously whileother measurements of biologically relevant attributes of a sample maybe made before or after the measurements that are made simultaneously.

In embodiments, one or more of such measurements may be rapidmeasurements, where a rapid measurement is one that may be made within atime period of about one hour; or may be made within a time period ofabout one half an hour; or may be made within a time period of about onequarter of an hour; or may be made within a time period of about tenminutes; or may be made within a time period of about 5 minutes; or maybe made within a time period of about 4 minutes; or may be made within atime period of about 3 minutes; or may be made within a time period ofabout 2 minutes; or may be made within a time period of about 1 minute;or may be made within a time period of about 30 seconds; or may be madewithin a time period of about 15 seconds; or may be made within a timeperiod of about 10 seconds; or may be made within a time period of about5 seconds; or may be made within a time period of about 1 second.

In embodiments, one or more of such measurements may be made using asmall volume blood sample, or no more than a small volume portion of ablood sample, where, a small volume blood sample, and a small volumeportion of a blood sample, comprises no more than about 5 mL; orcomprises no more than about 3 mL; or comprises no more than about 1 mL;or comprises no more than about 250 μL; or comprises no more than about100 μL; or comprises no more than about 50 μL; or comprises no more thanabout 25 μL; or comprises no more than about 20 μL; or comprises no morethan about 15 μL; or comprises no more than about 10 μL; or comprises nomore than about 5 μL; or comprises no more than about 1 μL; or comprisesother small volume, e.g., as described herein.

In embodiments of devices and systems disclosed herein, a device maycomprise a device for measuring both a) TC or a cholesterol sub-fractionin at least a portion of a sample of blood from a subject, and b)another attribute of said sample of blood from the subject. Inembodiments, said other attribute may be measured on a different portionof the sample of blood from the subject than the portion used to measureTC or a cholesterol sub-fraction. In embodiments, said other attributemay be measured on the same portion of the sample of blood from thesubject as is used to measure TC or a cholesterol sub-fraction. Inembodiments, a device for measuring both a) TC or a cholesterolsub-fraction in at least a portion of a sample of blood from a subject,and b) another attribute of said sample of blood from the subject maycomprise: means for combining a first reagent with at least a portion ofa sample of blood from a subject, effective to provide a combinedsolution; means for combining a second reagent with said combinedsolution to provide a colored solution; means for measuring an opticalproperty of said colored solution; means for displaying or reporting theresults of said measurement of said optical property of said coloredsolution; and means for measuring another attribute of said sample ofblood from the subject. In embodiments, a device for measuring both a)TC or a cholesterol sub-fraction in at least a portion of a sample ofblood from a subject, and b) another attribute of said sample of bloodfrom the subject may be configured for, and able to, make any two ormore of a plurality of measurements on a sample, such as a blood sample.In embodiments of a device for measuring both a) TC or a cholesterolsub-fraction in at least a portion of a sample of blood from a subject,and b) another attribute of said sample of blood from the subject, saidmeasurements may be selectable effective that some or all of a pluralityof measurements are selected for measurement of a first sample, and adifferent selection of some or all of said plurality of measurements maybe selected for measurements to be performed on a second sample.

In further embodiments, a device for measuring both a) TC or acholesterol sub-fraction in at least a portion of a sample of blood froma subject, and b) another attribute of said sample of blood from thesubject may comprise: a chamber for combining a first reagent with atleast a portion of a sample of blood from a subject, effective toprovide a combined solution; a conduit for combining a second reagentwith said combined solution to provide a colored solution; an opticaldetector for measuring an optical property of said colored solution; acentrifuge; and a display element or a communication link for reportingthe results of said measurement of said optical property of said coloredsolution. In embodiments of such a device, the device may be configuredfor, and able to, make any two or more of a plurality of measurements onthe sample. In embodiments of such a device, said measurements may beselectable effective that some or all of a plurality of measurements areselected for measurement of a first sample, and a different selection ofsome or all of said plurality of measurements may be selected formeasurements to be performed on a second sample.

Systems for measuring total cholesterol or a cholesterol sub-fraction inat least a portion of a blood sample, and another biologically relevantattribute from said blood sample from a subject may include a device formeasuring both a) TC or a cholesterol sub-fraction in at least a portionof a sample of blood from a subject, and b) another attribute of saidsample of blood from the subject. In embodiments, such a systemcomprises a device for measuring both a) and b) as disclosed herein, anda means for communicating information from said device to a computer, acomputer network, a telephone, a telephone network, or a deviceconfigured to display information communicated from said device. Inembodiments, a system for measuring both a) TC or a cholesterolsub-fraction in at least a portion of a sample of blood from a subject,and b) another attribute of said sample of blood from the subjectcomprises a device as disclosed herein, and a channel for communicatinginformation from said device to a computer, said wherein said channel isselected from a computer network, a telephone network, a metalcommunication link, an optical communication link, and a wirelesscommunication link. Systems as disclosed herein may comprise a deviceconfigured for, and able to, make any two or more of a plurality ofmeasurements on the sample. In embodiments of systems comprising such adevice, said measurements may be selectable effective that some or allof a plurality of measurements are selected for measurement of a firstsample, and a different selection of some or all of said plurality ofmeasurements may be selected for measurements to be performed on asecond sample.

Embodiments of systems for measuring total cholesterol or a cholesterolsub-fraction in at least a portion of a blood sample, and anotherbiologically relevant attribute from said blood sample from a subjectmay include a device as disclosed in U.S. Pat. No. 8,088,593 or U.S.application Ser. No. 13/244,947 filed Sep. 26, 2011, both fullyincorporated herein by reference for all purposes, and may includesystems as disclosed therein. For example, systems as disclosed hereinmay include a communication assembly for transmitting or receiving aprotocol based on the analyte to be detected or based on other analytesto be detected by the device or system. For example, in embodiments, anassay protocol may be changed based on optimal scheduling of a pluralityof assays to be performed by a device, or may be changed based onresults previously obtained from a sample from a subject, or based onresults previously obtained from a different sample from the subject. Inembodiments, a communication assembly may comprise a channel forcommunicating information from said device to a computer, said whereinsaid channel is selected from a computer network, a telephone network, ametal communication link, an optical communication link, and a wirelesscommunication link. In embodiments, systems as disclosed herein maytransmit signals to a central location, or to an end user, and mayinclude a communication assembly for transmitting such signals. Systemsas disclosed herein may be configured for updating a protocol as neededor on a regular basis.

Assays, methods, reagents, kits, devices, and systems as disclosedherein provide advantages over prior assays, methods, reagents, kits,and systems by allowing the rapid and inexpensive measurement ofcholesterol and cholesterol sub-fractions in a single assay. The methodsand assays disclosed herein allow for measurement of multiplelipoprotein fractions on the same sample of blood, or on the sameportion of a sample of blood; for example, HDL-C, LDL-C, and TC may bemeasured on the same sample of blood, or on the same portion of a sampleof blood. These measurements are made without substantial precipitationof lipoproteins in the sample, or sample portion. Providing desiredmeasurements in a single assay simplifies procedures, reduces likelihoodof error, reduces variability of results, and allows for more rapid andmore inexpensive procedures. The disclosed assays, methods, reagents,kits, and systems are effective to reduce the number of assays requiredto determine TC, HDL-C, LDL-C, and other cholesterol sub-fractions andblood lipoprotein components (e.g., VLDL-C and TG). Accordingly, theassays, methods, reagents, kits, devices, and systems disclosed hereinprovide improvements over the art.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an exemplary reaction scheme where cholesterol esters(e.g., as are found in lipoproteins in a sample of blood) may react witha cholesterol esterase to form cholesterol, which may react with acholesterol oxidase and oxygen to form hydrogen peroxide. Hydrogenperoxide, in the presence of horseradish peroxidase and colorants suchas an amino-antipyrene (e.g., 4-aminoantipyrene) and ananiline-containing compound (e.g.,N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline) may react toform a colored product (e.g., a Trinder (e.g., quinoneimine) dye asindicated in the figure).

FIG. 1B shows an exemplary reaction scheme where triglycerides (e.g., asare found in a sample of blood) may react with a lipase to form glyceroland fatty acids. The glycerol may be phosphorylated, in the presence ofadenosine triphosphate (ATP), by a glycerol kinase, and the resultingglycerol phosphate may be oxidized by glycerol-3-phosphate oxidase toprovide dihydroxyacetone phosphate and hydrogen peroxide. Hydrogenperoxide, in the presence of horseradish peroxidase and colorants suchas an amino-antipyrene (e.g., 4-aminoantipyrene) and ananiline-containing compound (e.g.,N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline) to form acolored product (e.g., a quinoneimine dye, or Trinder dye, as indicatedin the figure).

FIG. 2 plots sample lipid values found in lipoproteins, showing lipidvalue in units of milligrams per deciliter (mg/dL) along the verticalaxis versus the total cholesterol (as mg/dL) along the horizontal axis,where the lipid value and the total cholesterol were measured usingAdvia® Chemistry Systems reagents and methods (Siemens HealthcareDiagnostics, Inc., Tarrytown, N.Y.).

FIG. 3 plots assay kinetics for an exemplary experiment, where thedifference in absorbance of light by a solution containing sample,reagent A and reagent B at a wavelength of 560 nanometers (nm) and at awavelength of 700 nm (“Absorbance (A560-A700 mm)”) was measured byspectrophotometry. Absorbance at a wavelength of 560 nm was determinedby measuring the absorbance between 550 nm and 570 nm; absorbance at awavelength of 700 nm was determined by measuring the absorbance between690 nm and 710 nm. The time shown on the horizontal axis is time inminutes after the addition of Reagent B (the composition of Reagent B isdescribed in Table 2).

FIG. 4A shows LDL-C measurements using the kinetic data from a single,exemplary assay as disclosed herein, and plots the reported LDL-C,HDL-C, and TC values as determined by an assay as disclosed herein(where Reagent A is as described in Table 1 and Reagent B is asdescribed in Table 2) along the vertical axis (in units of mg/dL) versusthe LDL-C, HDL-C, and TC values (in mg/dL) determined by the dextransulfate assay using the Siemens Direct assay. The initial point near(0,0) in FIG. 4A does not represent experimental data, but was includedin the analysis and figures for clarity and to provide an anchor pointfor the fitted lines. FIG. 4A: LDL-C results (showing the difference inabsorbance measured at 6 minutes minus the absorbance measured at 2minutes).

FIG. 4B shows HDL-C measurements using the kinetic data from a single,exemplary assay as disclosed herein, and plots the reported LDL-C,HDL-C, and TC values as determined by an assay as disclosed herein(where Reagent A is as described in Table 1 and Reagent B is asdescribed in Table 2) along the vertical axis (in units of mg/dL) versusthe LDL-C, HDL-C, and TC values (in mg/dL) determined by the dextransulfate assay using the Siemens Direct assay.

FIG. 4C shows TC measurements using the kinetic data from a single,exemplary assay as disclosed herein, and plots the reported LDL-C,HDL-C, and TC values as determined by an assay as disclosed herein(where Reagent A is as described in Table 1 and Reagent B is asdescribed in Table 2) along the vertical axis (in units of mg/dL) versusthe LDL-C, HDL-C, and TC values (in mg/dL) determined by the dextransulfate assay using the Siemens Direct assay. The initial point near(0,0) in FIG. 4C does not represent experimental data, but was includedin the analysis and figures for clarity and to provide an anchor pointfor the fitted lines. FIG. 4C: TC results, absorbance measured at 10minutes.

FIG. 5 shows the results of an exemplary triglyceride assay as describedin Example 3, using Reagent AT and Reagent BT. Triglyceride levelsobtained using the present novel methods are presented as the Y-axisvalue of each diamond in the figure, and are plotted versus triglyceridemeasurements made using a prior art method (the X-axis value for eachdiamond). The data have been fitted with a straight line having a slopenear 1 (0.9536); the R² value of the least-squares fitting was 0.9537.

FIG. 6 shows comparisons of VLDL-C values, where the VLDL-C valuesobtained from prior art (ultracentrifugation) methods are plotted alongthe vertical axis, and VLDL-C values obtained from calculations based onHDL-C, TC, and TG measurements as disclosed herein. R squared (R²) andother values indicating the goodness of fit are shown in the figures.For the results of the measurements shown in FIG. 6, VLDL-C was bestcalculated by the relationship:

VLDL-C=0.152×TC+0.15×TG−0.549×HDL-C+0.0015×(TG-192)×(TC-188)−2.62

(where “x” indicates multiplication). As indicated in FIG. 6, for the 20data points shown in the figure, the VLDL-C values calculated accordingto the methods disclosed herein, i.e., by the equation above, agreedvery well with the VLDL-C values obtained by ultracentrifugation methods(R squared of 0.959).

DETAILED DESCRIPTION

Applicants have found that very accurate and precise values for TC,LDL-C and HDL-C can be obtained in a single assay for cholesterol usingkinetic measurements. Assays as disclosed herein may use a lipase,cholesterol esterase, cholesterol oxidase and a peroxidase to form acolored product measurable by spectrophotometry. In the assays disclosedherein, color formed from all the cholesterol-containing species isdirectly proportional to the quantity of cholesterol converted.

Description and disclosure of examples of reagents, assays, methods,kits, devices, and systems which may be used as disclosed herein may befound, for example, in U.S. Pat. No. 8,088,593; U.S. application Ser.No. 13/244,947; U.S. Application Ser. No. 61/673,037; U.S. ApplicationSer. No. 61/673,245; U.S. Application Ser. No. 61/675,758; U.S.Application Ser. No. 61/675,811; U.S. Application Ser. No. 61/676,178;U.S. Application Ser. No. 61/697,797; U.S. Application Ser. No.61/705,552; and U.S. Application Ser. No. 61/706,753; the disclosures ofwhich patent and patent applications are all hereby incorporated byreference in their entireties.

DEFINITIONS

Before the present formulations and methods of use are disclosed anddescribed, it is to be understood that the terminology used herein isfor the purpose of describing particular embodiments only and is notintended to be limiting. It is also to be understood that the presentdisclosure provides explanatory and exemplary descriptions and examples,so that, unless otherwise indicated, the assays, reagents, methods,devices, and systems disclosed herein are not limited to the specificembodiments described herein.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a surfactant” refers to a single surfactant or mixtures ofdifferent surfactants, and the like.

In this specification and in the claims that follow, reference will bemade to a number of terms, which shall be defined to have the followingmeanings:

As used herein, the terms “substantial” means more than a minimal orinsignificant amount; and “substantially” means more than a minimally orinsignificantly. Thus, for example, the phrase “substantiallydifferent”, as used herein, denotes a sufficiently high degree ofdifference between two numeric values such that one of skill in the artwould consider the difference between the two values to be ofstatistical significance within the context of the characteristicmeasured by said values. Thus, the difference between two values thatare substantially different from each other is typically greater thanabout 10%, and may be greater than about 20%, optionally greater thanabout 30%, optionally greater than about 40%, optionally greater thanabout 50% as a function of the reference value or comparator value.

As used herein, the terms “zwitterionic” and “dipolar” each refer tomolecules having charged groups of opposite polarity.

As used herein, the term “amphiphilic” refers to a compound or compoundshaving both hydrophobic and hydrophilic properties; typically, anamphiphilic molecule has a hydrophobic portion and also has ahydrophilic portion. A hydrophobic portion of a molecule may be anonpolar portion, relatively water-insoluble portion, such as ahydrocarbon chain portion. A hydrophilic portion of a molecule may be apolar, relatively water soluble portion, and may include an acidic orbasic moiety capable of gaining or losing a charge in water solution.Surfactants are typically amphiphilic compounds. Exemplary commerciallyavailable amphiphilic compounds include Triton™ surfactants,polyethylenesorbitans such as the TWEEN® compounds, and poloxamers(e.g., ethylene oxide/propylene oxide block copolymers) such asPluronics® compounds.

As used herein, a “surfactant” is a compound effective to reduce thesurface tension of a liquid, such as water. A surfactant is typically anamphiphilic compound, possessing both hydrophilic and hydrophobicproperties, and may be effective to aid in the solubilization of othercompounds. A surfactant may be, e.g., a hydrophilic surfactant, alipophilic surfactant, or other compound, or mixtures thereof. Somesurfactants comprise salts of long-chain aliphatic bases or acids, orhydrophilic moieties such as sugars. Surfactants include anionic,cationic, zwitterionic, and non-ionic compounds (where the term“non-ionic” refers to a molecule that does not ionize in solution, i.e.,is “ionically” inert). For example, surfactants useful in the reagents,assays, methods, kits, and for use in the devices and systems disclosedherein include, for example, Tergitol™ nonionic surfactants and Dowfax™anionic surfactants (Dow Chemical Company, Midland, Mich. 48642);polysorbates (polyoxyethylenesorbitans), e.g., polysorbate 20,polysorbate 80, e.g., sold as TWEEN® surfactants (ICI Americas, NewJersey, 08807); poloxamers (e.g., ethylene oxide/propylene oxide blockcopolymers) such as Pluronics® compounds (BASF, Florham Park, N.J);polyethylene glycols and derivatives thereof, including Triton™surfactants (e.g., Triton™ X-100; Dow Chemical Company, Midland, Mich.48642) and other polyethylene glycols, including PEG-10 laurate, PEG-12laurate, PEG-20 laurate, PEG-32 laurate, PEG-32 dilaurate, PEG-12oleate, PEG-15 oleate, PEG-20 oleate, PEG-20 dioleate, PEG-32 oleate,PEG-200 oleate, PEG-400 oleate, PEG-15 stearate, PEG-32 distearate,PEG-40 stearate, PEG-100 stearate, PEG-20 dilaurate, PEG-25 glyceryltrioleate, PEG-32 dioleate, PEG-20 glyceryl laurate, PEG-30 glyceryllaurate, PEG-20 glyceryl stearate, PEG-20 glyceryl oleate, PEG-30glyceryl oleate, PEG-30 glyceryl laurate, PEG-40 glyceryl laurate,PEG-40 palm kernel oil, PEG-50 hydrogenated castor oil, PEG-40 castoroil, PEG-35 castor oil, PEG-60 castor oil, PEG-40 hydrogenated castoroil, PEG-60 hydrogenated castor oil, PEG-60 corn oil, PEG-6caprate/caprylate glycerides, PEG-8 caprate/caprylate glycerides,polyglyceryl-10 laurate, PEG-30 cholesterol, PEG-25 phyto sterol, PEG-30soya sterol, PEG-20 trioleate, PEG-40 sorbitan oleate, PEG-80 sorbitanlaurate, polysorbate 20, polysorbate 80, POE-9 lauryl ether, POE-23lauryl ether, POE-10 oleyl ether, POE-20 oleyl ether, POE-20 stearylether, tocopheryl PEG-100 succinate, PEG-24 cholesterol,polyglyceryl-10oleate, sucrose monostearate, sucrose monolaurate,sucrose monopalmitate, PEG 10-100 nonyl phenol series, PEG 15-100 octylphenol series, and poloxamers; polyoxyalkylene alkyl ethers such aspolyethylene glycol alkyl ethers; polyoxyalkylene alkylphenols such aspolyethylene glycol alkyl phenols; polyoxyalkylene alkyl phenol fattyacid esters such as polyethylene glycol fatty acids monoesters andpolyethylene glycol fatty acids diesters; polyethylene glycol glycerolfatty acid esters; polyglycerol fatty acid esters; polyoxyalkylenesorbitan fatty acid esters such as polyethylene glycol sorbitan fattyacid esters; phosphocholines, such as n-dodecylphosphocholine, (DDPC);sodium dodecyl sulfate (SDS); n-lauryl sarcosine;n-dodecyl-N,N-dimethylamine-N-oxide (LADO); n-dodecyl-β-D-maltoside(DDM); decyl maltoside (DM), n-dodecyl-N,N-dimethylamine N-oxide (LADO);n-decyl-N,N-dimethylamine-N-oxide,1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC);1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC); 2-methacryloyloxyethylphosphorylcholine (MPC);1-oleoyl-2-hydroxy-sn-glycero-3-[phospho-RAC-(1-glycerol)] (LOPC);1-palmitoyl-2-hydroxy-sn-glycero-3-[phospho-RAC-(1-glycerol)] (LLPG);3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS);n-Octyl-N,N-dimethyl-3-ammonio-1-propanesulfonate;n-Decyl-N,N-dimethyl-3-ammonio-1-propanesulfonate;n-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate;n-Hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate;Tetradecanoylamidopropyl-dimethylammonio-propanesulfonate;Hexadedecanoylamidopropyl-dimethylammonio-propanesulfonate;4-n-Octylbenzoylamido-propyl-dimethylammonio Sulfobetaine; a Poly(maleicanhydride-alt-1-tetradecene), 3-(dimethylamino)-1-propylaminederivative; a nonyl phenoxylpolyethoxylethanol (NP40) surfactant;alkylammonium salts; fusidic acid salts; fatty acid derivatives of aminoacids, oligopeptides, and polypeptides; glyceride derivatives of aminoacids, oligopeptides, and polypeptides; lecithins and hydrogenatedlecithins, including lecithin, lysolecithin, phosphatidylcholine,phosphatidylethanolamine, phosphatidylglycerol, phosphatidic acid,phosphatidylserine; lysolecithins and hydrogenated lysolecithins;phospholipids and derivatives thereof; lysophospholipids and derivativesthereof, including lysophosphatidylcholine,lysophosphatidylethanolamine, lysophosphatidylglycerol, lysophosphatidicacid, lysophosphatidylserine, PEG-phosphatidylethanolamine,PVP-phosphatidylethanolamine; carnitine fatty acid ester salts; salts ofalkylsulfates; fatty acid salts; sodium docusate; acyl lactylates; mono-and di-acetylated tartaric acid esters of mono- and di-glycerides;succinylated mono- and di-glycerides; citric acid esters of mono- anddi-glycerides; lactylic esters of fatty acids, stearoyl-2-lactylate,stearoyl lactylate, succinylated monoglycerides, mono/diacetylatedtartaric acid esters of mono/diglycerides, citric acid esters ofmono/diglycerides, cholylsarcosine, caproate, caprylate, caprate,laurate, myristate, palmitate, oleate, ricinoleate, linoleate,linolenate, stearate, lauryl sulfate, teracecyl sulfate, docusate,lauroyl carnitines, palmitoyl carnitines, myristoyl carnitines, andsalts and mixtures thereof; alkylmaltosides; alkylthioglucosides; laurylmacrogolglycerides; hydrophilic transesterification products of a polyolwith at least one member of the group consisting of glycerides,vegetable oils, hydrogenated vegetable oils, fatty acids, and sterols;polyoxyethylene sterols, derivatives, and analogues thereof;polyoxyethylated vitamins and derivatives thereof;polyoxyethylene-polyoxypropylene block copolymers; and mixtures thereof;fatty alcohols; glycerol fatty acid esters; acetylated glycerol fattyacid esters; lower alcohol fatty acids esters; propylene glycol fattyacid esters; sorbitan fatty acid esters; polyethylene glycol sorbitanfatty acid esters; sterols and sterol derivatives; polyoxyethylatedsterols and sterol derivatives; polyethylene glycol alkyl ethers; sugaresters; sugar ethers; lactic acid derivatives of mono- anddi-glycerides; hydrophobic transesterification products of a polyol withat least one member of the group consisting of glycerides, vegetableoils, hydrogenated vegetable oils, fatty acids and sterols; oil-solublevitamins/vitamin derivatives; and combinations thereof.

As used herein, the term “solubilizing” refers to dissolving a moleculein a solution.

The term “lipoprotein solubilization agent” as used herein refers toagents that aid in maintaining lipoprotein particles in solution.Amphiphilic compounds such as surfactants may be suitable for use aslipoprotein solubilization agents in the reagents, assays, methods, andkits disclosed herein, and in the devices and systems for the practiceof such methods.

As used herein, a “colorant” is a compound (which may act alone or withother compounds) that is useful to alter an optical property of asolution, or to provide a new optical property to a solution. Forexample, a colorant may be may be a dye, a chromophore, a chromogeniccompound, a chemiluminescent compound, a fluorescent compound, afluorogenic compound (such as, e.g., Amplex red), a nanoparticle such asa quantum dot, or other element or compound which alters the opticalproperties of a solution. For example, a colorant may act, or mayparticipate in a reaction to, alter an optical property of a solution towhich it is added, or to provide or produce a luminescent, fluorescent,or other optically active product in the solution. An optical propertyof a solution may be, e.g., the color of a solution; the absorbance of asolution to a particular wavelength, range of wavelengths, orcombination of wavelengths, of light; the amount or peak wavelength ofluminescence or fluorescence of a solution; the turbidity of a solution;or any other property of a solution affecting the reflection, orabsorbance of light by a solution. As used herein, the term “colorant”also refers to a compound or result of a reaction that may alter theturbidity of a solution or the clarity of a solution. A colorant mayact, or may participate in a reaction to, change the absorbance of lightthrough a solution to which the colorant is added. It will be understoodthat “a colorant” may refer to a one molecule or class of molecules, ormay refer to a pair of molecules or classes of molecules that maytogether act to alter an optical property of a solution, or may refer tomultiple molecules or classes of molecules that may together act toalter an optical property of a solution.

A peroxidase that participates in a reaction with its substrate(s) toform a colored product is a colorant, as are substrates of theperoxidase. For example, the colorant horseradish peroxidase (HRP)participates in a reaction with any one or more of several moleculeseffective to change the optical properties of a solution to which theHRP is added (e.g., by changing the color, the absorbance of lightthrough a solution to which the HRP is added, and/or other opticalproperties of the solution). For example, HRP may react with ananiline-containing compound such asN-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (ALPS), or withan aminoantipyrene compound such as 4-aminoantipyrene or with phenoliccompounds. Thus, for example, a peroxidase (e.g., HRP, myeloperoxidase,or other peroxidase), an aniline-containing compound, and anaminoantipyrene may all be termed “colorants.” In further examples, HRPmay react with a benzidine-containing compound (e.g., withdiaminobenzidine (DAB); tetramethylbenzidine (TMB);2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (DABS);3-dimethylaminobenzoic acid (DMAB); hydroquinone; o-tolidine;o-phenylenediamine; o-chlorophenol; p-hydroxy-benzenesulfonate;p-anisidine; a Trinder reagent (such as 4-aminoantipyrene,methylbenzothiazolinonehydrazone (MBTH), or other compound for producinga Trinder dye); and derivatives and related compounds) to form a coloredproduct. HRP or other peroxidase may also react with other compounds toform a chemiluminescent product; for example, HRP or other peroxidasemay react with luminol to form a chemiluminescent product (othermolecules may be present, and may enhance such reactions; for example,HRP-mediated production of luminescent products from luminol is enhancedin the presence of 4-iodophenol). Other colorants include, for example,alkaline phosphatase; resazurin (7-Hydroxy-3H-phenoxazin-3-one10-oxide); 10-acetyl-3,7-dihydroxyphenoxazine (Amplex Red) and similarcompounds (e.g., Amplex UltraRed (A36006 from Life Technologies,Carlsbad, Calif. 92008); resorufin compounds (e.g., 7-ethoxyresorufin);dyes such as e.g., fluorescein, calcein, rhodamine, and ethidium dyes;N-methyl-4-hydrazino-7-nitrobenzofurazan; acridinium(acridine-9-carboxylic acid) esters and compounds which react with thesecompounds to alter an optical property of a solution; phenols and phenolderivatives (e.g., p-iodophenol and p-phenylphenol); luminescent amines,including amine adducts (e.g., as may be derived from copper cyanide),and other molecules. It will be understood that other enzymes andreactants may be used to form colored products, or to detect cholesterolin a blood sample.

As used herein, the terms “product formation,” “colored product,”“colored product formation,” and the like are used to refer to the actof, and the products that result from, addition of a colorant to asolution. For example, addition of a colorant to a solution may resultin a reaction effective to alter an optical property of the solution.Such a reaction may result in the formation of molecules originally notpresent in the solution, or may result in the aggregation of moleculesor compounds previously in the solution, or may result in thedegradation or other alteration of molecules or compounds previously inthe solution, effective to alter the color, absorbance, and/or otheroptical properties of a solution to which a colorant is added.

A sample, as used herein, is a biological specimen obtained from asubject, and may be, without limitation, a blood sample, a urine sample,a throat or cheek swab, a tissue sample, a sample of cerebrospinalfluid, or other sample which may be obtained from a subject. As usedherein, the term “a sample” includes a complete biological specimen andincludes a portion or an aliquot of a biological specimen, such as ablood draw taken from a subject. A sample is typically obtained foranalysis, e.g., for determination of one or more biologically relevantattributes such as, e.g., total cholesterol and/or other lipoproteinmeasurement; blood triglyceride (TG) level; hematocrit; pH, glucoselevel; uric acid level; salt concentration (e.g., of a cation and/oranion which makes up a salt); blood iron content; erythrocytesedimentation rate (ESR); a cytometric measurement (e.g., cell size,cell density, cell morphology, cell type, detection of cell surfaceand/or intracellular markers and attributes, etc.); a chemicalmeasurement including a measurement of the presence of and/orconcentration of a vitamin, a protein, a metabolite of a protein orsmall molecule, and other measurements of blood, urine, tissue, or otherbiological sample.

A sample, such as a blood sample, or a portion of a blood sample, may beof any suitable size or volume, and is optionally of small size orvolume. In some embodiments of the assays and methods disclosed herein,measurements may be made using a small volume blood sample, or no morethan a small volume portion of a blood sample, where a small volumecomprises no more than about 5 mL; or comprises no more than about 3 mL;or comprises no more than about 2 mL; or comprises no more than about 1mL; or comprises no more than about 500 μL; or comprises no more thanabout 250 μL; or comprises no more than about 100 μL; or comprises nomore than about 75 μL; or comprises no more than about 50 μL; orcomprises no more than about 35 μL; or comprises no more than about 25μL; or comprises no more than about 20 μL; or comprises no more thanabout 15 μL; or comprises no more than about 10 μL; or comprises no morethan about 8 μL; or comprises no more than about 6 μL; or comprises nomore than about 5 μL; or comprises no more than about 4 μL; or comprisesno more than about 3 μL; or comprises no more than about 2 μL; orcomprises no more than about 1 μL; or comprises no more than about 0.8μL; or comprises no more than about 0.5 μL; or comprises no more thanabout 0.3 μL; or comprises no more than about 0.2 μL; or comprises nomore than about 0.1 μL; or comprises no more than about 0.05 μL; orcomprises no more than about 0.01 μL.

As used herein, “lipoproteins” and “lipoprotein particles” include,without limitation, chylomicrons, very low density lipoprotein (VLDL),low density lipoprotein (LDL), and high density lipoprotein (HDL).Lipoproteins contain, among their multiple constituents, triglycerides(TG) and cholesterol, including cholesterol esters and other forms ofcholesterol. The cholesterol (in all its forms) within or attached tolipoproteins is termed VLDL-C, LDL-C, and HDL-C, respectively. The totalcholesterol (TC) of a blood sample includes the cholesterolsub-fractions VLDL-C, LDL-C, and HDL-C.

As used herein, “lipoprotein precipitation,” “precipitation oflipoproteins,” and similar terms refer to aggregation of lipoproteins(e.g., by exposure to divalent cations such as magnesium ions in thepresence of negatively charged polymers, e.g., negatively chargedpolysaccharides such as dextran sulfate) and may also refer tocentrifugation or other action to further separate lipoproteins fromother blood components. Substantial precipitation of lipoproteins mayoccur when a large fraction, such greater than about 75%, or greaterthan about 80%, or greater than about 85%, or greater than about 90%, orgreater than about 95%, or greater than about 99%, of the lipoproteinsin a sample of blood are aggregated or precipitated.

As used herein, the term “lipoprotein interactant” refers to a compound,or pair, or group of compounds, which may act to aggregate and/orprecipitate lipoproteins from a solution. It will be understood,however, that the term “lipoprotein interactant” is used herein as anidentifier, and that the use or inclusion of such compounds need notrequire precipitation of lipoproteins in a solution or during an assayin which lipoprotein interactants may be present. An exemplary form ofinteraction with a lipoprotein is mediated by cations, such as magnesiumand other divalent cations, where a negatively charged polymer, such asa negatively charged polysaccharide (e.g., a dextran sulfate) associateswith a lipoprotein via the charged cations. Thus, such cations as, forexample, magnesium (typically in the form of MgCl₂) may be termed“lipoprotein interactants.” Other lipoprotein interactants include,without limitation, dextrans, cyclodextrins, phosphotungstic acid,phosphotungstic acid salts (e.g., sodium phosphotungstate, includingsodium phosphotungstate with magnesium chloride), polyvinyl sulfate,heparins, heparin with manganese chloride, polyethylene glycols (e.g.,polyethylene glycol (PEG) 6000), and antibodies (such as, for example,anti-apolipoprotein-B-specific monoclonal antibodies). Antibodies aretypically used with centrifugation methods in lipoprotein assays.

Dextrans for use in methods and reagents as described herein may beobtained, for example, as dextran sulfate. Cyclodextrins, such asα-cyclodextrins, for use in methods and reagents as described herein maybe obtained, for example, as cyclodextrin sulfate. In some prior artmethods, lipoproteins may be precipitated from a blood sample byrelatively low concentrations of dextran sulfate and relatively highconcentrations of magnesium chloride (e.g., 0.182 μM dextran sulfate and32 mM MgCl₂ as described by Kimberly et al. (Clinical Chemistry45(10):18803-1812 (1999)).

As used herein, the term “dextran” refers to any form of a complex,branched glucan (that is, polysaccharide made of many glucose molecules)composed of polysaccharide chains of varying lengths. Linkages betweenglucose molecules along straight lengths of polysaccharide chains (e.g.,between branches) are typically α-1,6 glycosidic linkages, whilebranching linkages between glucose molecules are typically α-1,3glycosidic linkages. The sizes and molecular weights of dextrans varieswidely; for example, dextran polysaccharide chains may have widelyvarying lengths, and dextrans exhibit great variation in molecularweight (e.g., from about 3 kilodaltons (kD) to about 2000 kD or more).As used herein, the term “dextran” includes dextran esters and salts,such as, e.g., dextran sulfate salts, dextran acetate salts, dextranpropionate salts, dextran succinate salts, and other dextran salts.

It will be understood that a dextran molecule may be found, or may beprovided, in a heterogenous mixture containing different dextranmolecules each of which may have a different structure and/or adifferent molecular weight than other dextran molecules in a dextrancomposition such as a bulk composition of dextran. As used herein, theterms “dextran molecular weight,” “molecular weight of a dextran,” andsimilar terms refer to the average molecular weight of dextran moleculesin a bulk composition of dextran, and does not suggest that all, or evenmost, dextran molecules in a bulk composition of dextran have theparticular molecular weight identified as the “dextran molecularweight.” Thus, it will be understood that the molecular weight of adextran refers to an average value attributed to a bulk compositioncomprising a heterogenous mixture of dextran molecules which may vary intheir weight and structure.

As used herein, the term “low molecular weight dextran” refers to adextran in which the dextran molecular weight is less than about 100kilodaltons (kD), and is typically less than about 75 kD; inembodiments, a low molecular weight dextran may have a molecular weightof between about 25 kD and about 75 kD, or between about 40 kD and about60 kD. In embodiments, a low molecular weight dextran may have amolecular weight of about 50 kD.

As used herein, the term “cyclodextrin” refers to any cyclicpolysaccharide, e.g., a cyclic compound made up of sugar molecules. Thenumber of sugar molecules in the ring of a cyclodextrin may vary; forexample, cyclodextrins having six sugars in a ring are termedα-cyclodextrins; those having seven-membered rings are termedβ-cyclodextrins; and cyclodextrins having eight sugar molecules in aring are termed γ-cyclodextrins.

As used herein, a negatively charged polymer is any organic moleculecontaining repeating units and having a negative charge in watersolution at near neutral pH (e.g., pH between about pH 5 and about pH 9,optionally between about pH 6 and about pH 8). For example, polyvinylsulfate is a negatively charged polymer. Other negatively chargedpolymers include negatively charged polysaccharides, including heparinsand dextran esters.

Cholesterol may be measured in the blood of a subject, such as a humansubject. The cholesterol measured in a blood sample may be referred toas comprising cholesterol of one or more cholesterol sub-fraction. Asused herein, the term “total cholesterol” and its acronym “TC” is usedto indicate the total amount of cholesterol in a sample. Where theamount of cholesterol in a blood sample is discussed, and where nototherwise indicated, the term “cholesterol” refers to “totalcholesterol.” Cholesterol may be found in many forms in the blood of asubject (e.g., a human subject); for example, cholesterol may be foundin the blood in chylomicrons, in VLDL, in LDL, and/or in HDL. Each ofchylomicrons, VLDL, LDL, and HDL may be termed a cholesterolsub-fraction. The sum of the amounts of cholesterol present in thechylomicron, VLDL, LDL, and HDL sub-fractions makes up the totalcholesterol in a sample of blood obtained from a subject.

The total amount of cholesterol, and the amounts of cholesterol inindividual, and in each, cholesterol sub-fraction, may be measured by avariety of means know in the art, and by the novel methods and meansdisclosed herein. As used herein, the term “cholesterol measurementdata” refers to the data resulting from measurements of cholesterol in asample, and may refer to measurements of TC, VLDL-C, LDL-C, HDL-C,chylomicron cholesterol, and combinations thereof, without limitation.For example, as disclosed herein, cholesterol may be measured by anysuitable means, including amperommetry, voltammetry, or other means,including by measuring an optical property of a blood sample, such as ablood sample following addition of a reagent or reagents according tomethods and assays disclosed herein. For example, as disclosed herein,cholesterol may be measured by measuring absorbance in a blood sample,e.g., in a blood sample following addition of a reagent or reagentsaccording to methods and assays disclosed herein. In embodiments,cholesterol measurement data comprises data obtained by measuringabsorbance using a spectrophotometer. In embodiments, cholesterolmeasurement data comprises data obtained by measuring ΔA using aspectrophotometer, where ΔA is the difference between absorbancemeasured at two wavelengths, such as, e.g., between about 560 nm andabout 700 nm. Thus, for example, cholesterol measurement data may beobtained by measuring ΔA using a spectrophotometer, by measuringabsorbance at a wavelength of about 560 nm and at a wavelength of about700 nm, and calculating or otherwise obtaining the difference betweenthese absorbance measurements.

The term “absorbance” is used herein according to its usual andcustomary meaning in the art, and refers to the optical property of asolution (e.g., a sample) related to the ratio of the amount of optical(e.g., electromagnetic) radiation falling upon a solution to the amountof optical radiation transmitted through the solution (e.g., thesample).

Absorbance may be measured by measuring the amount of light absorbedduring passage through a medium, by measuring the amount of light thatpasses through a medium, or by other method known in the art.Transmittance (T) is typically defined as the ratio of the amount oflight passing through a sample to the amount of light passing through acontrol (e.g., a blank), where the amount of light is typically measuredby light intensity. The amount of light that fails to pass through themedium is thus 1−T. The absorbance A is typically defined as thenegative log₁₀ of T. Thus, absorbance and transmittance are measuredtogether, as determination of one of these values allows determinationof the other value. Thus, as used herein, “absorbance” also indicatesand refers to “transmittance” as determination of absorbance allows forthe determination of transmittance as well.

As used herein, absorbance (and transmittance) may be measured within aparticular range of wavelengths, or at a particular wavelength, or atmultiple particular wavelengths. Absorbance measured at a particularwavelength may be obtained by measurements within a range of wavelengthscentered around that particular wavelength. For example, absorbance at560 nm may be obtained by measuring absorbance between wavelengths ofabout 530 nm to about 590 nm; by measuring absorbance betweenwavelengths of about 540 nm to about 580 nm; optionally by measuringabsorbance between wavelengths of about 550 nm to about 570 nm; orbetween other wavelengths greater and lesser than 560 nm. Similarly,absorbance at 700 nm may be obtained by measuring absorbance betweenwavelengths of about 670 nm to about 730 nm; by measuring absorbancebetween wavelengths of about 680 nm to about 720 nm; optionally bymeasuring absorbance between wavelengths of about 690 nm to about 710nm; or between other wavelengths greater and lesser than 700 nm.Absorbance was measured using a spectrophotometer in the Examplesdisclosed herein.

As used herein, the term “ΔA” refers to the difference in absorbancemeasured at a first wavelength and absorbance measured at a secondwavelength; for example, a first wavelength may be about 560 nm and asecond wavelength may be about 700 nm. For example, ΔA may be measuredby the difference in absorbance measured at a wavelength of about 560 nmand at a wavelength of about 700 nm, and calculating or otherwiseobtaining the difference between these absorbance measurements. Thus,for example, such a ΔA measured at 560 nm and 700 nm may be termed “ΔA(560-700 nm).”

As used herein, the term “spectrophotometer” refers to a deviceconfigured for, and effective to, measure optical intensity within aparticular range of wavelengths, or at a particular wavelength, or atmultiple particular wavelengths. A spectrophotometer may be effective tomeasure absorbance in a sample. A spectrophotometer may be effective tomeasure light emitted from a sample (e.g., fluorescence and/orluminescence). A spectrophotometer may be effective to measureabsorbance in a sample and to measure light emitted from a sample.

As used herein the term “spectrophotometry” refers to the making ofmeasurements using a spectrophotometer; e.g., to the making of opticalmeasurements within a particular range of wavelengths, or at aparticular wavelength, or at multiple particular wavelengths.

As used herein, the term “optical detector” and means for measuring anoptical property (e.g., of a colored solution) refer to any suitableoptical means, optical device, photodetector, and optical device elementfor detecting electromagnetic radiation (e.g., light of any wavelength).For example, an optical detector, and optical detection means, may beused to detect absorbance, transmittance, turbidity, luminescence(including chemiluminescence), fluorescence and/or other optical signal.Optical detectors include, but are not limited to, imaging devices.Optical means, optical devices, photodetectors, and optical deviceelements include, but are not limited to, electronic detectors such asdigital cameras, charge coupled devices (CCDs, including super-cooledCCDs), photodiodes (including, e.g., pin diodes and avalanchephotodiodes), photomultipliers, phototubes, photon counting detector,arrays of photodiodes (including, e.g., pin diode arrays and avalanchephotodiode arrays), arrays of charge coupled devices (includingsuper-cooled CCD arrays), arrays of photodiodes, arrays ofphotomultipliers, arrays of phototubes, arrays of photon countingdetectors, and other detection devices and detection elements. In someembodiments a pin diode or other element may be coupled to an amplifier.

In some embodiments, an optical detector may include a camera (e.g., adigital camera). A camera may include a lens, or may operate without alens. In some instances, cameras may include CCDs, may use complementarymetal-oxide semiconductor (CMOS) elements, may be lensless cameras,microlens-array cameras, open-source cameras (including, e.g., aFrankencamera as described by Levoy, “Experimental Platforms forComputational Photography,” IEEE Computer Graphics and Applications,Vol. 30, No. 5, September/October, 2010, pp. 81-87) and may use anyvisual detection technology known or later developed in the art. Camerasmay acquire conventional and/or non-conventional images, e.g.holographic images, tomographic images, interferometric images,Fourier-transformed spectra, any or all of which may be interpreted withor without the aid of computational methods. Cameras may include one ormore feature that may focus the camera during use, or may capture imagesthat can be later focused. In some embodiments, imaging devices mayemploy two-dimensional (2-D) imaging, three-dimensional (3-D) imaging,and/or four-dimensional (4-D) imaging (incorporating changes over time).Imaging devices may capture static images. Optical schemes used toachieve 3-D and 4-D imaging may be one or more of the several known tothose skilled in the art, e.g. structured illumination microscopy (SLM),digital holographic microscopy (DHM), confocal microscopy, light fieldmicroscopy etc. Static images may be captured at one or more point intime. Imaging devices may capture video and/or dynamic images. Videoimages may be captured continuously over a single period, or may becaptured over one or more periods of time. An imaging device may collectsignal from an optical system which scans a target (e.g., a sample usedfor an assay) in arbitrary scan patterns (e.g., in a raster scan).

An optical detector, and optical detection means, include withoutlimitation, a microscope, and means for optical detection may includemicroscopy, visual inspection, via photographic film, or may include theuse of electronic detectors such as digital cameras, charge coupleddevices (CCDs), super-cooled CCD arrays, phototubes, photodetectors, andother detection devices known in the art, and as disclosed herein. Anoptical detector, and optical detection means, may include an opticalfiber or a plurality of optical fibers (e.g., fiber optic cables) whichmay, for example, be functionally connected to a CCD detector or to aPMT array. A fiber optic bundle may comprise discrete fibers and/or manysmall fibers fused together to form a solid bundle.

An optical detector may include a light source, such as an electricbulb, incandescent bulb, electroluminescent lamp, laser, laser diode,light emitting diode (LED), gas discharge lamp, high-intensity dischargelamp, a chemiluminescent light source, a bioluminescent light source, aphosphorescent light source, a fluorescent light source, and naturalsunlight. In embodiments, e.g., where chemiluminesence is to bedetected, light may be produced by the assay chemistry. In embodiments,a light source can illuminate a component in order to assist withdetecting the results. For example, a light source can illuminate asolution in assay in order to detect the results of the assay. Forexample, an assay can be a fluorescence assay or an absorbance assay, asare commonly used with nucleic acid assays. A detector may compriseoptical elements effective to deliver light from a light source to anassay or assay chamber. Such an optical element may include, withoutlimitation, for example, a lens, a mirror (e.g., a scanning orgalvano-mirror), a prism, a fiber optic fiber or bundle of fibers, alight guide (e.g., a liquid light guide), and/or other optical element.An optical detector may include such optical elements, where suchoptical elements are disposed effective to deliver light to a detector.For example, an optical detector may be configured to detect selectedwavelengths or ranges of wavelengths of electromagnetic radiation. Anoptical detector may be configured to move over, or to view portions of,a sample. An optical detector may include a mirror, a motor, apiezoelectric element, or other element effective to allow detection oflight from different portions of a target location at different times,e.g., to scan a sample.

An optical detector may be used to detect one or more optical signal.For example, a detector may be used to detect the presence of, orprogress of a reaction providing luminescence. A detector may be used todetect a reaction providing one or more of fluorescence,chemiluminscence, photoluminescence, electroluminescence,sonoluminescence, absorbance, turbidity, optical-rotary-dispersion(ORD), circular dichroism (CD), or polarization. An optical detector maybe able to detect optical signals relating to color intensity and phaseor spatial or temporal gradients thereof.

As used herein, a means for communicating information from said deviceto a computer or other external device, and a channel for communicatinginformation to a computer or other external device, without limitationrefers to a computer network, a telephone, a telephone network, and adevice configured to display information communicated from said device.In embodiments, a means for communicating information, and a channel forcommunicating information include direct links using wires (includingtwisted pair, coaxial, ribbon, and other cables), wireless means andwireless technology (e.g., Bluetooth technology or RTM (retransmissionmode) technology). Communicating means and channels for communicationinclude any suitable communication method, including a dial-up wiredconnection with a modem, a direct link using a wire, a wirelessconnection including infrared, cellular, wimax, wifi, satellite, pager,general packet radio service (GPRS), local data transport system (suchas, e.g., ethernet or token ring over a local area network (LAN) orother network).

An external device to be communicated with may be any device capable ofreceiving such a communication. For example, an external device may be anetworked device, including a server, a personal computer, a laptopcomputer, a tablet, a mobile device, a “dumb” cell phone, a satellitephone, a smart phone (e.g., iPhone®, Android™, Blackberry®, Palm,Symbian, Windows®), a personal digital assistant (PDA), a pager or anyother device. In embodiments, an external device may be a diagnosticdevice. In some embodiments where an external device comprises adiagnostic device, the relationship between devices and systemsdisclosed herein and an external device may comprise a master-slaverelationship, a peer-to-peer relationship, or a distributedrelationship.

As used herein, the term “lipase” refers to a class of enzymes thatcatalyze reactions with a lipid as a part of the reaction substrate.Lipases may catalyze reactions such as hydrolysis or other reactions.For example, a lipase may catalyze a reaction where a cholesterol esteris metabolized to cholesterol and a fatty acid.

As used herein, the term “cholesterol esterase” refers to an enzymeeffective to catalyze a reaction that removes or alters an ester bond,such as a carboxylic acid ester, of a cholesterol molecule orcholesterol moiety of a cholesterol-containing molecule. Cholesterolesterases (also known as “sterol esterases” and as “bile lipases”)typically catalyze a reaction in which a steryl ester combines withwater to form a sterol and a fatty acid. Cholesterol esterases arecommon, and may be found in single-cell and in multi-cellular organisms;many commercially useful cholesterol esterases are bacterial cholesterolesterases, although cholesterol esterases from other sources are knownand are useful as well. For example, a useful cholesterol esterase maybe a bacterial cholesterol esterase, such as a cholesterol esteraseobtained from Gram-negative bacteria, including a cholesterol esterasefrom a Pseudomonas species.

As used herein, the term “cholesterol oxidase” refers to an enzymeeffective to catalyze a reaction in which a cholesterol molecule or acholesterol moiety of a cholesterol-containing molecule combines withoxygen to form an oxidized cholesterol moiety such as cholest-4-en-3-one(also forming hydrogen peroxide). Many cholesterol oxidases arebacterial cholesterol oxidases. For example, a useful cholesteroloxidase may be a cholesterol oxidase, such as may be obtained fromGram-negative bacteria, including a cholesterol oxidase from aPseudomonas species.

As used herein, a “buffer” is a compound or group of compounds which, insolution, tend to maintain the pH of the solution at or near aparticular value. For example, phosphate salts may be used as buffers.Phosphate salts include NaH₂PO₄, Na₂HPO₄, and Na₃PO₄. Other buffers arealso suitable for use in the reagents, assays and methods disclosedherein, including without limitation citrate, ammonium, acetate,carbonate, tris(hydroxymethyl)aminomethane (TRIS), 3-(N-morpholino)propanesulfonic acid (MOPS), 3-morpholino-2-hydroxypropanesulfonic acid(MOPSO), 2-(N-morpholino)ethanesulfonic acid (IVIES),N-(2-Acetamido)-iminodiacetic acid (ADA),piperazine-N,N′-bis(2-ethanesulfonic acid) (PIPES),N-(2-Acetamido)-2-aminoethanesulfonic acid (ACES), cholamine chloride,N,N-Bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES),2-[[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]amino]ethanesulfonic acid(TES), 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid (HEPES),acetamidoglycine, tricine(N-(2-Hydroxy-1,1-bis(hydroxymethyl)ethyl)glycine), glycinamide, bicine(2-(Bis(2-hydroxyethyl)amino)acetic acid), and other buffers. Any buffermay be used as long as it buffers a water solution at the desired pH andis otherwise compatible with the assays and methods disclosed herein. Inembodiments, a buffer may be used to buffer the pH of a solution in a pHrange of near neutral pH to slightly acidic pH, for example, from aboutpH 5 to about pH 9, or between about pH 6 to about pH 8, or betweenabout pH 6.8 to about pH 7.8, and in embodiments, to a pH of about pH 7or of about pH 7.4.

The novel methods and assays disclosed herein make use of Applicants'finding that cholesterol sub-species are converted to the measuredproduct at distinct rates. Accordingly, HDL-C is converted very rapidlyto product, while LDL-C is converted to product more slowly than HDL-Cis converted to product and VLDL-C and chylomicrons are converted evenmore slowly. Complete conversion of total cholesterol to product is evenslower than the conversion of HDL-C or LDL-C to product. Suchdifferences in rates of conversion to product allow the measurement ofcholesterol from different lipoprotein species to be made in a singlesolution at different times, thus reducing the number of steps neededfor such measurements, reducing possible errors and simplifying theprocedures. In embodiments disclosed herein, “product” may be a coloredproduct, such as, e.g., a colored product formed by a peroxidase such ashorseradish peroxidase. By making measurements of colored product at,for example, (1) very early times (for example, 0-2 minutes), atsomewhat later times (for example, 2-6 minutes) and at late time (forexample, 10 minutes or later) the two most important cholesterol subfractions (HDL-C and LDL-C) and total cholesterol (T-C) can be measuredin a single assay. Importantly, since the assay is performed in a singlereaction mixture, the ratios of cholesterol sub-fractions to totalcholesterol are determined more accurately and precisely than would beexpected by performing several different assays in different reactionmixtures. Additionally, assays and methods disclosed herein, beingperformed in a single reaction mixture, can significantly reduce thecosts of cholesterol measurements as compared to the costs of priormethods and assays which require running three or more assays to obtaincholesterol sub-fraction and total cholesterol values.

Methods and assays disclosed herein make use of the differential ratesat which each cholesterol-containing lipoprotein fractions are acted onby a lipase (e.g., a cholesterol esterase) and an oxidase (e.g., acholesterol oxidase). The lipoproteins differ in the composition of thelipids they contain (e.g., lipids including triglycerides, cholesterol,cholesterol esters, and phospholipids) and in the apo-lipoproteins thathelp solubilize lipids for transport through blood. Lipoproteins arevery heterogeneous but the fractions thought to be of most utility inassessing lipid status for clinical diagnostic purposes are sufficientlydistinct in their physical and chemical properties, and have beendistinguished in prior art methods by the rates at which they move undercentrifugal force or when subject to electrophoretic separation.

In contrast to prior art methods, the assays and methods disclosedherein utilize, and the reagents disclosed herein provide, conditions inwhich HDL, LDL, and VLDL lipoproteins react with the assay chemistry atsufficiently different rates in the same solution without substantialprecipitation so that each fraction can be measured in a single assayusing multiple measurements at different times. Thus in one example ofmethods disclosed herein HDL-C is completely consumed by about twominutes while LDL-C requires about six minutes to be completelyconverted to measured product. By waiting somewhat longer (e.g., tenminutes, or longer) all the cholesterol in the sample is converted.According to the methods disclosed herein, total cholesterol can beestimated at the assay end-point by measuring the absorbance of thecolored product. According to the methods disclosed herein, LDL-C can bemeasured by taking the rate of color production over a range of time(for example 2-6 minutes). During the earliest part of the reaction(e.g., 0-2 minutes) both HDL and LDL are being consumed; thecontribution of HDL can be estimated using the LDL concentrationmeasured within the assay (e.g., once the LDL concentration is knownfrom measurements made with the assay). As disclosed herein, a methodfor doing the calculation has been established. The present methods thusallow the use of rate data alone to compute HLD-C and LDL-C and Total-C.LDL-C may be calculated from kinetic data taken from the middle part ofthe assay reaction (e.g., measurements taken at about 2 to 6 minutesafter initiation of the assay) and HDL-C may be estimated from the earlypart (e.g., about 0 to 2 minutes after initiation of the assay) of thereaction allowing for the contribution of LDL.

Applicants have found that one aspect of assays disclosed hereininvolves setting up assay conditions (e.g., reagents, protocol andtemperature) so that, in the same solution without substantialprecipitation of lipoproteins, the kinetics of reactions convertingHDL-C, LDL-C, chylomicrons, and VLDL-C to colored product proceed atsignificantly different rates while allowing essentially completereaction of all lipoprotein species (e.g., HDL, LDL, and VLDL) beforethe end of the assay. The reagents and methods disclosed herein providethe conditions which allow the differentiation over time betweendifferent lipoprotein fractions in a single reaction mixture withoutsubstantial lipoprotein precipitation.

For example, under the conditions disclosed herein, the time course forHDL-C has a half-time estimated at less than one minute whereas theLDL-C conversion has a lag phase and an overall sigmoid shape centeredon about three minutes. Under the conditions disclosed herein, theremaining lipoprotein cholesterol (chylomicrons and VLDL-C) reacts evenmore slowly (e.g., with a half-time of about five minutes or longer).These differences in half-time and reaction kinetics between differentlipoprotein cholesterol species enable the de-convolution of the assaysignal to that attributable to each species using a simple algorithmeven though, for example, signal is being produced from more than onespecies during certain times during the assay. Thus, the methodsdisclosed herein allow rapid, convenient, and accurate determination ofcholesterol in the major lipoprotein fractions.

In conventional prior art assays LDL and VLDL are precipitated by one ofa variety of reagents. For example, dextran sulfate and magnesium ionscan bridge the negatively charged lipoprotein particles so theyaggregate to form, for example, LDL:Mg²⁺:Dextran sulfate:Mg²⁺:LDLcomplexes. Precipitate formation in such conventional assays requiresparticular concentrations of both reagents in the correct ratios.Precipitates in such conventional assays can then be removed bycentrifugation or filtration. Other LDL and VLDL precipitating reagentsare known such as phosphotungstic acid, polyvinyl sulfate, Heparin withManganese Chloride, Polyethylene glycol (PEG) 6000, SodiumPhosphotungstate with Magnesium Chloride andanti-apolipoprotein-B-specific monoclonal antibodies.

In contrast, reagent formulations for use in the assays and methodsdisclosed herein are designed to achieve the kinetic differentiationdescribed above without requiring precipitation of any lipoproteins. Inreagents disclosed herein, complex formation with magnesium and dextransulfate is achieved in conditions in which essentially no precipitationof lipoproteins occurs. A variety of surfactants and other reagents suchas α-cyclodextrin are suitable for use in keeping the lipoproteinssoluble. The LDL and VLDL particle surfaces are modified in such a wayas to restrict but not prevent access to LDL and VLDL cholesterol andcholesterol esters. The use of reagents and methods suitable for suchmodification of LDL and VLDL particle surfaces is effective to slow theformation of colored product from these lipoprotein species.

One exemplary reagent composition shown below in Table 3 uses a lowermolecular weight dextran sulfate and a much higher magnesium ionconcentration and ratio of magnesium ions to dextran sulfate as comparedto prior art predicate methods. In the first step in the assay theconcentrations of these ingredients are reduced to half due to additionof sample in both the present and predicate methods.

It will be understood that the particular ingredients and their amountsmay vary in the reagents used in the practice of the methods disclosedherein. The reagent compositions shown in Table 3 provide one example ofmany possible reagents that are suitable for use in these methods. Ingeneral, the reagents will include cations, and the cations in reagentssuitable for use in these methods will optionally be divalent cations,such as magnesium, manganese, calcium, barium, and other divalentcations. In embodiments of the reagents for use in the methods disclosedherein, the divalent cation concentration will be in the range of about0.1 mM to about 20 mM, optionally between about 1 mM to about 10 mM, oroptionally between about 2 mM and about 8 mM. In general, the reagentswill include negatively charged polysaccharides, and the negativelycharged polysaccharides in reagents suitable for use in these methodswill optionally be dextran esters, such as dextran sulfate. Inembodiments of the reagents for use in the methods disclosed herein, theamount of negatively charged polysaccharide (e.g., dextran sulfate) willbe in the range of about 0.1 g/L to about 20 g/L, optionally betweenabout 0.3 g/L to about 10 g/L, or optionally between about 0.5 g/L andabout 5 g/L. In particular embodiments of reagents suitable for use inthe methods disclosed herein, the negatively charged polysaccharides(e.g., dextran sulfate) will have molecular weights in the range ofbetween about 10,000 to about 1,000,000, optionally in the range ofbetween about 20,000 to about 500,000, optionally in the range ofbetween about 25,000 to about 100,000, or optionally in the range ofbetween about 30,000 to about 80,000. In particular embodiments ofreagents suitable for use in the methods disclosed herein, the ratio ofnegatively charged polysaccharides (e.g., dextran sulfate) to divalentcations will be in the range of between about 0.001 to about 0.1,optionally in the range of between about 0.001 to about 0.05, optionallyin the range of between about 0.002 to about 0.02, or optionally in therange of between about 0.003 to about 0.007.

In the examples disclosed herein, control (“predicate”) measurements ofcholesterol and cholesterol sub-fraction were made using Advia®chemistry and methods using an Advia® 1800 machine per the suggestedinstructions provided by the maker and supplier of the Advia® products,Siemens Healthcare Diagnostics (Tarrytown, N.Y. 10591 USA).

Accordingly, as described above, reagents, assays and methods providingnegatively charged polysaccharides (such as dextran esters, e.g.,dextran sulfate), optionally negatively charged cylodextrins (such asα-cyclodextrin sulfate), and cations (e.g., divalent cations such asmagnesium) in the combined reagents with a blood sample during the assayafter an initial time as discussed above, effective to provide differentrates of degradation of cholesterol from different lipoprotein fractionsso that measurement of the progress of the reaction at different timesand/or during different time periods, as discussed above, is effectiveto measure and determine HDL-C, LDL-C, VLDL-C, and/or TC.

In alternative embodiments of the reagents, assays, and methodsdisclosed herein, a lipase (e.g., a cholesterol esterase), adehydrogenase (e.g., a cholesterol dehdrogenase) and nicotine adeninedinucleotide (NAD) may be combined during an assay, e.g., a blood samplemay be added to a reagent, or mixture of reagents, so that the bloodsample, the lipase, the dehydrogenase, and NAD (e.g., in its oxidizedform NAD⁺) are all present in a solution effective that the lipase mayact to release cholesterol from cholesterol esters in lipoproteins inthe sample, and the dehydrogenase and nicotine adenine dinucleotidereact effective to provide a reduced form of nicotine adeninedinucleotide (NADH) and cholest-4-en-3-one or other form of cholesterol,effective to provide a colored product (e.g., NADH) or other detectableproduct. In such alternative embodiments, similar amounts of negativelycharged polysaccharides (such as dextran esters, e.g., dextran sulfate),optionally negatively charged cylodextrins (such as α-cyclodextrin), andcations (e.g., divalent cations such as magnesium) are present in thereagents and in the combined reagents during the assay after an initialtime as discussed above, effective to provide different rates ofdegradation of cholesterol from different lipoprotein fractions so thatmeasurement of the progress of the reaction at different times and/orduring different time periods, as discussed above, is effective tomeasure and determine HDL-C, LDL-C, VLDL-C, and/or TC.

Thus, in such alternative embodiments, nicotine adenine dinucleotide isa colorant. The NADH may be detected by spectrophotometric or othermeans, as discussed above, effective that the levels of cholesterol maybe detected and measured. For example, NADH may be detected and itslevels determined by absorbance measurements at 340 nm or in awavelength range centered about 340 nm. NADH may be excited by lighthaving a wavelength of about 340 nm, and emits light with wavelengths ofabout 440 nm; thus NADH may be detected by excitation at about 340 nmand measuring emission at about 440 nm. Other methods for detecting andmeasuring NADH levels (e.g., to determine cholesterol levels in a bloodsample) include measurement of NADH formation using redox sensitivemolecules such as tetrazolium salts in the presence of a redox mediatorsuch as diaphorase; amperometric methods; and luminogenic methods whichconsume NADH (e.g., using luciferase-mediated light production, such asby use of a bacterial luciferase).

It is to be understood that while the above disclosure has beendescribed in conjunction with the specific embodiments thereof, that thedescription above as well as the examples that follow are intended toillustrate and not limit the scope of the invention. Other aspects,advantages and modifications within the scope of the invention will beapparent to those skilled in the art to which the invention pertains.

EXAMPLES Example 1 Chemistry and Reagents

Cholesterol Assay Chemistry:

Assays disclosed herein may be used to form colored product fromreactions with cholesterol and cholesterol derivatives (e.g.,cholesterol esters) found in a blood sample. As shown in FIG. 1,cholesterol esters may react with a cholesterol esterase to provide freecholesterol. Free cholesterol may react with a cholesterol oxidase andoxygen to form hydrogen peroxide. The hydrogen peroxide formed in such areaction may be used to quantify the amount of cholesterol in thesample. Hydrogen peroxide may react with a peroxidase to form a coloredproduct, e.g., in the presence of a colorant, or by use of a colorant,and such a reaction can be detected and quantified. For example,hydrogen peroxide, in the presence of horseradish peroxidase andcolorants such as aminoantipyrene compounds (e.g., 4-aminoantipyrene)and N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline, reacts toform a colored product (e.g., a Trinder (quinoneimine) dye as indicatedin FIG. 1).

Cholesterol Assay Reagents:

Compositions for two exemplary reagents, AC and BC, are listed Tables 1and 2 below. Reagent AC provides an example of a first reagent asdisclosed herein, and Reagent BC provides an example of a second reagentas disclosed herein. Reagents AC and BC may have compositions asdisclosed in Table 1A and 1B:

TABLE 1A Composition of Reagent AC Component Concentration cyclodextrin0.1 mM-10 mM (e.g., an α-, β-, or γ-cyclodextrin, as, e.g., a sulfate orphosphate) Negatively charged Dextran (50,000 MW) 0.1 g/L-20 g/L (e.g.,as sulfate or phosphate) Magnesium salt (e.g., chloride, sulfate,   1mM-10 mM acetate, carbonate, or other salt) 4-Aminoantipyrene 1-5 mMNa_(x)PO₄   20 mM-300 mM (pH between about pH 6-pH 8, e.g., pH 7.4)

TABLE 1B Composition of Reagent BC Component Concentration Na_(x)PO₄  10 mM-200 mM (pH between about pH 6-pH 8, e.g., pH 7.4) Triton X-100(octylphenol ethoxylate) 0.01%-1%  Pluronic L64 (polyethylene glycol-0.5 g/L-20 g/L polypropylene glycol co-block polymer) ALPS 0.5 mM-20 mMHorseradish Peroxidase 0.5 kU/L-20 kU/L Cholesterol Esterase fromPseudomonas sp.   100 U/L-5000 U/L Cholesterol Oxidase from Pseudomonassp. 0.25 kU/L-10 kU/L 

Where “ALPS” isN-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline, and“Na_(x)PO₄” is NaH₂PO₄, Na₂HPO₄ and Na₃PO₄ in ratios effective toprovide a pH of between about pH 6 to about pH 8.5; e.g., about pH 7.4.

For example, in particular embodiments, Reagents AC and BC may have thefollowing compositions as listed in Tables 2A and 2B below:

TABLE 2A Composition of Reagent AC Component Concentrationα-cyclodextrin sulfate 1 mM Dextran Sulfate (50,000 MW) 1 g/L MagnesiumChloride 4 mM 4-Aminoantipyrene 2.25 mM Na_(x)PO₄ pH 7.4 100 mM

TABLE 2B Composition of Reagent B Component Concentration NaxPO₄ pH 7.450 mM Triton X-100 (octylphenol ethoxylate) 0.06% Pluronic L64(polyethylene glycol- 3 g/L polypropylene glycol co-block polymer) ALPS3 mM Horseradish Peroxidase 3 kU/L Cholesterol Esterase from Pseudomonassp. 750 U/L Cholesterol Oxidase from Pseudomonas sp. 1.5 kU/L

Where “ALPS” isN-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline, and“Na_(x)PO₄” is NaH₂PO₄, Na₂HPO₄ and Na₃PO₄ in ratios effective toprovide a pH of between about pH 6 to about pH 8.5, e.g., about pH 7.4.

Table 3 provides a comparison of the amounts of dextran sulfate andmagnesium chloride used in the novel reagents and assays disclosedherein, and the amounts of dextran sulfate and magnesium chloride usedin prior art methods. In some prior art assays, dextran sulfate andmagnesium chloride may be used to precipitate lipoproteins during assaysfor cholesterol and cholesterol-esters. As illustrated in Table 3, thepresent assays include different concentrations of dextran sulfate andmagnesium chloride, so that there is substantially no precipitation oflipoproteins in the present assays.

TABLE 3 Comparison of some reagent-component concentrations. PresentNovel Assays Predicate Method^(‡) Interactant (Concentration)(Concentration) Dextran Sulfate 1 g/L  0.0091 g/L Magnesium 4 mM   32 mMChloride ^(‡)Predicate method: dextran sulfate-magnesium chloride methodof Kimberly et al., Clinical Chemistry 45(10): 1803-1812 (1999).

Example 2—Cholesterol Assays

1) At 37° C., 304, sample (neat plasma or serum diluted 1:30 in water orphosphate buffered saline (PBS)) was combined with 204, Reagent AC in awell of a 384-well microplate reader (MTP).

2) The plate was shaken for 2 seconds at 1800 rpm.

3) The plate was incubated at 37° C. for 5 minutes.

4) 20 μL Reagent BC was added. The plate was shaken for 2 seconds at1800 revolutions per minute (rpm).

5) The plate was incubated at 37° C. for 12 minutes in aspectrophotometer capable of reading absorbance at given time intervals.

6) Absorbance (A) was recorded at 560 nm and 700 nm every 30 seconds (anM5 spectrophotometer (Molecular Devices, Sunnyvale, Calif.) was used tomake the measurements). Note that other intervals, including longerintervals, are also suitable.

Samples:

FIG. 2 shows the lipid content of lipoproteins as measured in theclinical serum samples (including results for triglycerides) used forthe studies shown in the examples. As can be seen, there was poor to nocorrelation between the cholesterol in the various lipoproteinsub-forms. Also, the cholesterol levels spanned the range seen in normalsubjects and those with lipemia and so provided a good test set for themethods of the invention. In the data below, samples were also analyzedby a reference method using the Advia® Chemistry System (SiemensHealthcare Diagnostics, Inc., Tarrytown, N.Y.).

Time Course of the Cholesterol Assay Reaction:

Color formation occurs in the present cholesterol assay method inseveral phases. Examples of such phased color formation is illustratedin the results obtained for a sample measured in an exemplaryexperiment, as presented in FIG. 3 (times refer to the time after addingreagent BC). The phases included:

1. A rapid phase (0 to about 2 minutes) when HDL-C and LDL-C wereconsumed.

2. A sigmoidal process corresponding to a slight “lag” followed by arapid rise in color formation (about 2-about 6 minutes) when theremaining LDL-C were consumed.

3. A relatively slow consumption of VLDL-cholesterol (about 6-10 minutesor more) in a third phase.

Measurement of Lipoprotein Species by the Present Method andCorrelations with Results of Reference Methods:

In some cases commercially available control materials were alsomeasured. TC was measured using ΔA (560-700 nm) at ten minutes. LDL-Cwas measured by the difference in ΔA (560-700 nm) which occurred betweentwo and six minutes. HDL-C was measured by ΔA_(t), the change in ΔA(560-700 nm) which occurred between zero and two minutes. (ΔA is thedifference between the absorbance measured at 560 nm and the absorbancemeasured at 700 nm.) In the experiments of the present example, ΔA wasmeasured by a M5 spectrophotometer (Molecular Devices, Sunnyvale,Calif.).

Measurements labeled “Reference assay” were made using the SiemensAdvia® chemistry and methods (Siemens Healthcare Diagnostics, Inc.).

The following correlations were obtained which meet clinical assayrequirements:

LDL-Cholesterol: For 15 samples and controls: y=0.989*x; R²=0.978; xrange: 7.7-230 mg/dL; x mean=118.1; Standard error of theestimate/Mean=6.8%

HDL-Cholesterol: For 10 samples: y=0.98*x+1.35; R²=0.98; x range40.3−103.4 mg/dL; x mean 67.2 mg/dL; Standard error of theestimate/Mean=4.0%

Total cholesterol: for 14 samples and controls: y=0.977*x; R²=0.980; xrange 15-304 mg/dL; x mean=195.6 mg/dL; Standard error of theestimate/Mean=4.3% (where * indicates multiplication).

These results from the present and reference methods are shown ingraphic form in FIG. 4. The LDL-C results from the present and referencemethods are shown in FIG. 4A in graphic form. The HDL-C results from thepresent and reference methods are shown in FIG. 4B in graphic form. TheTC results from the present and reference methods are shown in FIG. 4Cin graphic form.

The formula for calculating HDL-C was derived by using the estimate ofthe LDL-C from the same assay plus the rate measured between 0 and 2minutes (where the * indicates multiplication):

HDL-Cholesterol=1.30-0.446*LDL-C+1255.5*(ΔA(560-700 nm),2min−(ΔA(560-700 nm),0 min)

The formula for calculating HDL-C was derived by using the estimate ofthe LDL-C from the same assay plus the rate measured between 0 and 2minutes (where the * indicates multiplication):

HDL-Cholesterol=1.30-0.446*LDL-C+1255.5*(ΔA(560-700 nm),2min−(ΔA(560-700 nm),0 min)

Both factors (LDL-C and (ΔA (560-700 nm), 2 min−(ΔA (560-700 nm), 0 min)were highly significantly correlated (p<0.0001).

The above equation was derived by multiple regression analysis of assayresults presented herein using trial and error combinations of themeasured absorbances, TC and LDL-C calculated from the absorbance data.

Conclusion: Use of specific reagent formulations and kinetic measurementof reaction product enable simultaneous measurement of total, LDL andHDL cholesterol.

Example 3 Triglyceride Assays

Triglyceride (TG) levels may be measured by an assay in whichtriglycerides in a sample are broken down into their constituent fattyacids and glycerol, and the glycerol levels measured photometrically asindicated in FIG. 1B. Glycerol may be phosphorylated by glycerol kinasein the presence of adenosine triphosphate (ATP), and the resultingglycerol phosphate oxidized by glycerol 3-phosphate oxidase to producedihydroxyacetone phosphate and hydrogen peroxide. The hydrogen peroxide,with horseradish peroxidase (or other peroxidase) can react withcolorants to produce a dye which can be measured by a spectrophotometerto determine the triglyceride content of the sample. Exemplary reagentsReagent AT and Reagent BT for use in this TG assay are shown in Table 4.As shown in the present example, 4-aminoantipyrene withN-Ethyl-N-(3-sulfopropyl) aniline will react with horseradish peroxidasein the presence of hydrogen peroxide to form a purple quineoneimine dye;the amount of dye formed can be determined by measuring absorbance at560 nm, as indicated in the procedure below, and as shown in theexperimental results reported in FIG. 5.

Triglyceride Assay Reagents

This assay uses an enzyme reaction cascade with results in theproduction of hydrogen peroxide (H₂O₂) which is used by HorseradishPeroxidase (HRP) to produce a purple color product. The reagents used insuch assays include a Reagent AT and a Reagent BT. Examples ofcompositions suitable for such reagents are shown in Table 4A, and thecompositions of particular specific exemplary Reagents AT and BT areshown in Table 4B.

TABLE 4A Triglyceride Assay Reagents Reagent AT Components ConcentrationRange Adenosine-5′-triphosphate (ATP) salt 0.1 mM to 10 mM (sodium,potassium, acetate, other salt) Magnesium salt (e.g., chloride, 0.5 mMto 50 mM sulfate, acetate, carbonate, or other salt) Lipase 1000 to1,000,000 U/L (e.g., a bacterial lipase) Surfactant (e.g., a Triton ™, a0.01% to 5%  TWEEN ® or a Pluronic ® surfactant) Buffered saline (e.g.,phosphate,      1 to 300 mM HEPES, or MOPS buffered solution) Reagent BTComponents Concentration Peroxidase (e.g., from horseradish,   150 U/Lto 15,000 U/L HRP) 4-aminoantipyrene (4-AA) 0.1 mM to 10 mMN-Ethyl-N-(3-sulfopropyl)aniline, 0.4 mM to 40 mM sodium salt (ALPS)Glycerol-3-Phosphate Oxidase (GPO)   100 U/L to 20,000 U/L Glycerokinase(GK)    5 U/L to 5000 U/L (e.g., from bacteria) Buffered saline (e.g.,phosphate,   1 mM to 300 mM HEPES, or MOPS buffered solution)

Particular exemplary Reagents AT and BT may be made according to theingredients and amounts as set out in Table 4B.

TABLE 4B Triglyceride Assay Reagents Concentration Reagent AT ComponentsAdenosine-5′-triphosphate (ATP) 1.5 mM disodium salt Magnesium Chloride(MgCl₂), 20 mM anhydrous Lipase from Chromobacterium 400,000 U/Lviscosum Octyl Phenol Ethoxylate (e.g., 0.3% Triton X-100 ®) PBS withTween 20 ® Diluted to “1X” (~10 mM K_(x)PO₄, ~138 mM NaCl, ~2.7 mM KCl,~0.05% Tween 20 ®) Reagent BT Components Horseradish Peroxidase (HRP)5,000 U/L 4-aminoantipyrene (4-AA) 1 mMN-Ethyl-N-(3-sulfopropyl)aniline, 4 mM sodium salt (ALPS) Glycerol3-Phosphate Oxidase 5,000 U/L (GPO) from microorganism Glyerokinase (GK)from 250 U/L Cellulomonas sp. PBS with Tween20 ® Diluted to “1X” (~10 mMK_(x)PO₄, ~138 mM NaCl, ~2.7 mM KCl, ~0.05% Tween 20 ®)

Exemplary Assay Procedure for Triglycerides in Blood Serum ofEDTA-Anticoagulated Plasma:

1. Samples (and/or calibrators) were diluted 1:30 with water.

2. Reagents and diluted samples were brought to 37° C. prior to theassay.

3. 20 μL, each of diluted sample, reagent AT and reagent BT as describedin Table 4B were mixed in the wells of a 384-well microtiter plate.

4. The mixture of diluted sample, reagent AT and reagent BT as describedin Table 4B were incubated at 37 C for 10 minutes.

5. Absorbance at 560 nm was read in a microtiterplate reader (MolecularDevices M5) following step 4.

TG measurements made according to the above-described methods are shownin FIG. 5 (the measurements providing the position of the data pointsalong the vertical axis); the data points are plotted versus TGmeasurements according to a prior art method (the method suggested byTeco Diagnostics, using the reagents of the commercially available Tecokit (Teco Diagnostics, Anaheim, Calif. 92807)). TG measured by thepresent methods agreed very closely with prior art TG measurements. Ifthere had been perfect agreement between the prior art and presentmethods, the slope of the line drawn through these points would give aslope of 1. As shown in FIG. 5, the slope of the line drawn by linearregression through these points had a slope very near to one(slope=0.9536). Thus, the TG determination methods shown in this examplecorrelate very well with those of other well-accepted methods.

Example 4 Combined Blood Cholesterol and Triglyceride Measurements

Measurements of cholesterol (C) and triglycerides (TG) may be made onaliquots of the same sample of blood, or on separate samples of bloodtaken from the same patient, in order to provide more complete clinicalinformation than would be available from measurement of C alone or of TGalone. In addition, TG measurements can be used to provide a measure ofthe VLDL in the blood sample. Thus, measures of LDL-C, HDL-C, TC,VLDL-C, and TG may be obtained by the methods of Examples 1, 2, and 3,and estimating VLDL-C by the formula:

VLDL-C=TG/5.

TC may be measured directly according to the methods and assaysdisclosed herein; similarly, HDL-C and LDL-C may be measured directlyaccording to the methods and assays disclosed herein. Since TC is ameasure of the total of the cholesterol in a sample, TC is the sum ofthe cholesterol in the lipoprotein fractions in the sample, and so maybe estimated by the relation TC=HDL-C+LDL-C+VLDL-C. Accordingly, byrearranging, a better determination of VLDL-C may be obtained from themeasured amounts of HDL-C, LDL-C, and TC as follows:

VLDL-C=TC−HDL-C−LDL-C

and may be determined by according to the methods and formulas asdescribed herein.

As discussed above, further methods for determining VLDL-C from themeasured values of HDL-C, LDL-C, and TC, and from the measured values ofTG, HDL-C, LDL-C, and TC, are disclosed herein. For example, inembodiments, the level of VLDL-C in a single sample, or a single portionof a sample, of blood of a subject may be calculated by the followingrelation:

VLDL-C=αTC+βHDL-C+γLDL-C+δTG+a ₁(TG+ε)(TC+κ)+λ

where α, β, γ, δ, and a₁ are constants which multiply TC, HDL-C, LDL-C,TG, and the cross-term (TG+ε)(TC+κ) respectively (in a cross-term, theterms in one parenthesis multiply the terms in the other parenthesis);and where ε, κ, and λ are additive constants to be added to TG, TC, andthe sum of all other factors, respectively. In a particular embodiment,where γ=0, the level of VLDL-C in a single sample, or a single portionof a sample, of blood of a subject may be calculated from thesemeasurements, for example, by the relation:

VLDL-C=αTC+βHDL-C+δTG+a ₁(TG+ε)(TC+κ)+λ

where α, β, δ, and a₁ are constants which multiply TC, HDL-C, TG, and(TG+ε)(TC+κ), respectively; and where ε, κ, and λ are additive constantsto be added to TG, TC, and the sum of all other factors, respectively.

An example of such a calculation of VLDL-C is shown in FIG. 6, where 20values of VLDL-C determined by the equation above based on measurementsas disclosed herein (plotted along the y-axis) are plotted versuscorresponding VLDL-C measurements made by prior art ultracentrifugationmethods (plotted along the x-axis). As shown in FIG. 6, the VLDL-Cvalues calculated according to the formula above quite accurately trackthose obtained by prior art methods. In the plot shown in FIG. 6, λ(“intercept”) has a value of −2.62; α has a value of 0.15; β has a valueof −0.55; δ has a value of 0.15; a₁ has a value of 0.0015; ε has a valueof −192; and κ has a value of −188. The VLDL-C values calculated by theequation above agree very well with the VLDL-C values obtained byultracentrifugation methods (R squared 0.959). The best fit line shownin the figure was calculated using JMP software (SAS institute, Inc.,Cary N.C., 27513), and analysis of variance for this model and theseparameters had an F ratio of 93.4 indicating that such a good fit wouldbe found by chance with a probability of less than 0.001, a highlysignificant result.

While the above is a description of the embodiment as described herein,it is possible to use various alternatives, modifications andequivalents. It should be understood that as used in the descriptionherein and throughout the claims that follow, the meaning of “a,” “an,”and “the” includes plural reference unless the context clearly dictatesotherwise. Also, as used in the description herein and throughout theclaims that follow, the meaning of “in” includes “in” and “on” unlessthe context clearly dictates otherwise. Finally, as used in thedescription herein and throughout the claims that follow, the meaningsof “and” and “or” include both the conjunctive and disjunctive and maybe used interchangeably unless the context expressly dictates otherwise.Thus, in contexts where the terms “and” or “or” are used, usage of suchconjunctions do not exclude an “and/or” meaning unless the contextexpressly dictates otherwise.

This document contains material subject to copyright protection. Thecopyright owner (Applicant herein) has no objection to facsimilereproduction of the patent documents and disclosures, as they appear inthe US Patent and Trademark Office patent file or records, but otherwisereserves all copyright rights whatsoever. The following notice shallapply: Copyright 2012 Theranos, Inc.

1-20. (canceled)
 21. A reagent for use in a cholesterol assay, saidreagent comprising a lipoprotein solubilization agent, lipoproteininteractant, and a buffer, wherein said lipoprotein interactant ispresent at a concentration level that provides for conversion of highdensity lipoprotein cholesterol (HDL-C) to a measureable colored productat a substantially different rate than for conversion of low densitylipoprotein cholesterol (LDL-C) to a measureable colored product and ata substantially different rate than for conversion of very low densitylipoprotein cholesterol (VLDL-C) to a measureable colored product whensaid reagent is used in a cholesterol assay.
 22. The reagent of claim21, comprising α-cyclodextrin sulfate, dextran sulfate, magnesiumchloride, 4-aminoantipyrene and a sodium phosphate buffer.
 23. Thereagent of claim 21, said reagent comprising magnesium and dextransulfate in a ratio of dextran sulfate to magnesium ions effective thatthere is no substantial precipitation of low-density lipoprotein (LDL),or that there is no substantial precipitation of very low-densitylipoprotein (VLDL), or both, when a blood sample containing LDL or VLDLis put in contact with said reagent.
 24. The reagent of claim 23,wherein said ratio of dextran sulfate to magnesium ions is between about0.002 to about 0.02.
 25. The reagent of claim 21, wherein saidlipoprotein solubilization agent is selected from a surfactant, and anegatively charged α-cyclodextrin derivative; and said lipoproteininteractant comprises a low molecular weight negatively charged dextranderivative. 26-30. (canceled)
 31. The reagent of claim 22, wherein saidratio of dextran sulfate to magnesium ions is between about 0.002 toabout 0.02.
 32. The reagent of claim 25, wherein said ratio of dextransulfate to magnesium ions is between about 0.002 to about 0.02.
 35. Thereagent of claim 21, wherein said lipoprotein solubilization agent is anonionic surfactant or a zwitterionic surfactant.
 36. The reagent ofclaim 21, wherein said lipoprotein interactant is a dextran derivative.37. A kit comprising a reagent and instructions for the use of saidreagent in a cholesterol assay, the reagent comprising α-cyclodextrinsulfate, dextran sulfate, magnesium chloride, 4-aminoantipyrene and asodium phosphate buffer.
 38. The kit of claim 37, wherein the ratio ofdextran sulfate to magnesium ions in the reagent is between about 0.002to about 0.02.